No it doesn't do anything different, except add a direct shortcut, to the base games Vampire.exe
If you click on Base exe, you get the "Legacy" game, but it's not really the pure Vanilla game.

Originally mods were added to the Vampire Folder, and you needed a separate game install for each Overhaul.

Then about 2015 Behar and Psycho-A released the Game Mod Loader, which allowed overhauls to add their own game folder
So now GOG game has the Unofficial Patch as, a built in overhaul
The Legacy shortcut runs runs without most of the UP changes.
"<Path To Your Game>\Vampire.exe"

UP is installed to "Unofficial_Patch" folder, so it's shortcut is
"<Path To Your Game>\Vampire.exe" -game Unofficial_Patch

Every Overhaul mod can now be installed in it's own folder (No spaces allowed in name) in one game install, with the generic path
"<Path To Your Game>\Vampire.exe" -game <ModFolderName>

I currently have seven overhauls in my only game install, rather than the seven installed games, of the old method.

But be clear "Legacy" is not actually a 100% pure Vanilla game, and to get it to true vanilla you need to remove all the extraneous UP changes, as well. That is pretty much a broken game, and the only reason for doing this is to patch the game without using UP.

See the link answering this question, as to why you would ever want the Pure Vanilla game, and how to get it.
Some people here have claimed that the TPG doesn't work with the legacy version?

I think it is, only exceptions being the hardware related fixes in the exe and dlls that remove e.g. the not anymore supported Safedisk protection and the 2 GB RAM limit.

You'll likely know better than me, I just remember getting an unofficial GOG made vanilla_cleaner.cmd script back when VTMB first arrived on GOG, which I think came with UP basic v9.6 originally

in fact I still have it, but a couple of things seem to have changed

I've just installed the UP basic v10.6 files to a folder only containing only the Vampire.exe file (Needed to get it running), to see exactly what's installed. by the installer.

That script seems to be mostly reinstating the original files you back up, with *,12 extensions
It also deletes4 folders
Unofficial_Patch
Bin\loader
Vampire\resource
Vampire\maps\graphs
So those would be simple to revert

The UP Basic 10.6 install shows these files added to Vampire Folder
Vampire\pack103.vpk
Vampire\pack102.vpk
Vampire\maps\graphs\ (101 *.ain files added)
Vampire\python\vamputil.py
Vampire\python\warrens\warrens.py
Vampire\resource\optionssubgameplay.res
Vampire\resource\optionssubvideo.res
Vampire\resource\trackerscheme.res
Vampire\resource\gameui_english.txt

These have no backup, unlike the DLL/EXE files, does that mean they are not part of the Vanilla game.

Only difference I can see to the script, is two *.pak files, and two *.py files.
So deleting those, as well seems to cover it, assuming no Vanilla files are replaced without making a backup.

Don't get me wrong, I think the UP is great, but I like to start modding from the pure vanilla game, and while I understand why GOG added the UP, to get the game running for none mod users.

I just like to mod from a pure vanilla base game myself, and know which files come from which mods.

That would be a bad idea in the first place, because you shouldn't be able run the old 12 extension files on a modern system as Windows doesn't recognize SafeDisk anymore if you use retail CDs and you probably have more than 2 GB RAM installed! This is correct. All the patch files should be in there! This again isn't good, as it removes executable improvements like native widescreen support and much more. The resource folder files are needed for the Game Mod Loader widescreen support and by removing the graphs folder you will get annoying AI node rebuilding messages on each map! It seems whoever made that script didn't really know what he was doing... ... because these are the official 1.2 patch files which are included in the UP, except for the resource folder files, see above. I wouldn't do that, the last guy who did this got something like "Why are all the typos back?" basically among the first comments ;). All other mayor Bloodlines mods are based on the basic patch for a reason! You can still revert anything there that you don't like...

I don't want to run the game using the .12 files, I.m fully aware the game is unplayable in that state.
My purpose is to use it as my starting point, and the basis for adding mods, from the original state.
This is how I mod every GOG game, starting from a pure Vanilla install, and I don't need GOG providing old versions of mods for me.

GOG comes with UP Basic v10.2, I want that old version completely removed, and game reverted to the base Vanilla state.

That script was created to enable users to choose which Patch they want to use, UP, or TGP
Except if using TGP, and the VTMB Mega-Mod that requires it, the very first mod I will install will be the latest UP Plus, because it's pretty much required, and the Game Mod Loader is already included, (but that could be installed separately without UP, if desired).

Key thing is, I don't want GOG making mod choices for me, even if a choice is required to run the game, on the general principal that stores should provide the Vanilla game, the whole game, and nothing but the game.

So I start modding from the base Vanilla game, and see no reason to change that for VTMB.

Also, I won't complain to you, If I mess my game up,
I've just done that installing the new AI HD textures over my already modded setup, and can't get past the Main menu anymore, it's my mistake, and that's why I'm back here reverting a fresh installed game to Vanilla once again.

Then maybe you should get the Steam version instead, they didn't add anything except their DRM. The main argument to choose GOG over Steam is that they make sure old games bought there will run on modern setups. You must be pretty hard-core then ;)! What kind of mod are you planning?

I don't think the Steam version works without creating a non-steam folder - it's basically incompatible with Bloodlines.
Also, if Win10 is involved, you can't turn off the Windows update that they added to prevent playing older games. But, of course, you know this :)

What Windows 10 update prevents playing older games exactly? I have win 10 and I can run VTMB without a problem. Though I do hate how Win 10 forces updates onto one every month, which sometimes messes with graphics drivers which in turn causes some games to not work (though so far this has only affected modern games, funnily enough).

There was a Windows 7-10 update that removed support for some old DRM systems like SecuROM and SafeDisk. Which was fixed in the UP for anybody still running the retail game and I guess Steam already replaced those with its own DRM code earlier...

When did Steam do this? I might be going on old info. Last I heard, if the UP wasn't used on Steam, one had to create a separate folder (which is what I assume you did in the patches).

Yes, the UP is not included in the Steam version. What I meant is that Steam replaced SecuROM with their own DRM so when Windows 10 removed it it didn't matter to the Steam version.

Ah OK. I actually thought that support for those old DRM systems were already gone (or at least pretty dodgy) with older Windows versions?

I've grabbed non-CD/DVD versions (such as from GOG) of all my old games a while ago, so that's probably why I didn't notice this change (I honestly didn't think old SecuROM/SafeDisk stuff worked on Windows 10 at all in the first place).

I think when MS disabled support for Windows 10 they did the same for Windows 7.

That's what I think too only with Win8 and Win7, you can make a manual change that reactivates support but this isn't possible with Win10.

Oh, I didn't know that.