Mac directions:
copy/pasta with edits Running Hacked designs 1. Download
uashellc.zip from the UA archive and extract its contents to your main UA directory 'D&D Unlimited Adventures.app/Contents/Resources/game' (Right-click Show Package Contents on the App to browse from Finder).
1b.
OPTIONAL: Code check removal (Pt. 1): If you want to permanently remove the obsolete codeword check from your legit copy of the game, also download
ckit-crk.zip and extract CKIT-CRK.COM to your main UA directory 'D&D Unlimited Adventures.app/Contents/Resources/game'.
2. Edit
script_alt.sh at 'D&D Unlimited Adventures.app/Contents/Resources' with a text editor. Change lines 5-6 to:
3. Make a copy of the file
dosbox_ua_single.conf in the same directory, 'D&D Unlimited Adventures.app/Contents/Resources/game', and rename it to
dosbox_uashell.conf. Open
dosbox_uashell.conf with a text editor. Find the line that says „start“ and replace it with „CALL uashell“.
3b.
OPTIONAL: Code check removal (Pt. 2): Insert a line
above „CALL uashell“ and put „ckit-crk“ in it (it's very important that your config file runs ckit-crk.com
before calling uashell or it won't work!). You can also remove GOG’s copy protection notice by deleting all lines from „@ECHO OFF“ to „pause“.

Gydion: Rest of
the directions are the same. Hold down <ALT> while launching the game to run UAShell.
You can swap the contents of
script.sh &
script_alt.sh to have it default to UAShell vs Standard. You can also do all this from Terminal if preferred.
You'll have to clarify about the last part, I'm trying to install UAShell but no matter what I try it doesn't work.
Leroux: ATTENTION! :)
Since the forum software has become even buggier in recent years, I don't dare to edit my original posts anymore, but there actually is a new and much easier way to apply hacked designs in FRUA now than the UAShell installation I described in 2015, at least for Windows, I guess. It's actually been available since 2017, and I overlooked it so far (my apologies!).
UA DESIGN APPLY by Donnie Ewald
uadap.zip Readme (Your anti-virus program may complain about it because it's a small unknown exe, but its fine, and my AVG gave me the okay after sending it to the test lab.)
How it works is you give it the path of your FRUA folder with the CKIT.exe in it and the folder of the design you wish to apply and press Apply, then exit and start FRUA. If you want to apply another design, you first press Revert to restore the original FRUA version, then Apply again with the path of your new design. Simple as that. Basically the same thing that UAShell did, but as a Windows program without complicated installation. (see screenshot)