Note: This method is not recommended. Also, this is assuming that level drain/gain abuse is either impossible or not used.

The idea is this:
1. Create the character as a Human Ranger with 18 Constitution in Secret of the Silver Blades
2. Level up the character to level 10 (exactly). Do not level the character up to level 11.
3. Dual class the character into fighter.

The math works like this:
Level 10 fighter gets 9d10 HP for levels 1-9 (max 9 * 14 = 126 at 18 CON), and 3 per level beyond that. That yields 129 HP at level 10.
Level 10 ranger gets 11d8 HP for levels 1-10 (max 11 * 12 = 132 at 18 CON), and 2 per level beyond that. That yields 132 HP at level 10, but less at higher levels.

By dual classing at level 10, we get ranger HP for levels 1-10 and fighter (or paladin) HP for levels 11-40. As a result, the character ends up with 3 more HP than if the character is a straight fighter.

Whether it is worth the effort for just 3 HP is an interesting question, and I suspect the answer may be no.

Is there anything I said here that is incorrect?

By the way, for level drain/gain abuse, the scheme (which I have not tested in any of the games) is as follows:
1. Make sure the character's level isn't too high to roll hit dice.
2. Intentionally level drain the character. If the character loses a lot of hit points, reload.
3. Regain the level. If the character doesn't gain more HP than she lost from the drain, reload.
4. Repeat steps 2 and 3. If this trick works, it should allow you to gain arbitrarily high HP. Does it?

My God, the lengths some people will go to...it's really mind boggling...

But why stop there? Why not just hex edit the CON up tp 20, or even 25?

This is just a theory topic. I will probably not actually do this when I get around to playing the games. (I might test is level drain/gain works in these games.)

Also, there's no guarantee that CON of 25 will work as expected. It will only work if the developers actually programmed data for CON that high.

It sounds like your interest lies more in breaking the games than playing them.

I remember creating a paladin and dual classing to ranger in CotAB at level 9 for getting a ranger with extra HP. She never gained the extra half attack she was supposed to get at ranger level 15, neither in SotSB nor in PoD.

Ranger10/Paladin might also be broken.

That leads to some interesting questions.

Does this bug occur if you replace Paladin with Fighter?
If you go Paladin->Ranger at level 13, do you lose a half attack? Or does the game give you another half attack at level 15, giving you 5/2 attacks? (That would be a nice exploit if it works that way.)
If you go Ranger->Paladin at level 13 or 14, do you lose a half attack when your paladin level passes your ranger level?

It's possible, of course, that the game may use only your Paladin level if you're a Paladin/Ranger. If that's true, then these cases would work, and Ranger 10/Paladin would not be broken (but Fighter 10/Paladin might be).

Of course, some testing is needed to check what actually happens. (The rule that you can't gain 2 levels at once becomes annoying in this context.)

Nearly all your posts are about finding and abusing game mechanics, rather than actually playing the games.

So?

It's a game. If he wants to manipulate the mechanics, let him have fun. You never mass-produced your magic items when you were a teenager? Or ran a courier to get around the item destruction in Pools of Darkness?

No, I've always found it more interesting to make the games more challenging, not abuse the mechanics and use tricks that were not intended to make the game too easy. Unless the games are really hard, that is (which the GB games aren't).
Oh well, each to their own, I guess. After all, some kids have nore fun brealking their toys than playing with them.

I think the only tinkering I did with the GB games was messing with the character files so that I could keep Princess Fatima first time I played Pool of Radiance.

IF you're willing to put in the game play, you can have human characters, raise them up to 9th fighter, the dual class them, for all your non-fighter characters. You can really pile on the XP in hillsfar (creating all the characters in por, giving all 18s and 18/100 strength, thne porting to hillsfar, then after level 9 transfer to por or curse to start their dual class)

What, no chainmail-bikini-with-a-beard character portrait in Pool of Radiance? Didn't everyone do that when they were 13?