Has anybody had any luck changing this GMST (Game Setting) value in a mod? I have a personal mod that changes several Game Settings including this one and does other things, but I am not seeing the change to this record when I play the game. I tried changing it from the default value of 5 to 10, but the setting of 5 is still in effect when I play. I know my mod is getting loaded because I'm seeing the other changes, such as changing the value of iMaxPlayerRunes from 1 to 3.

I've tried changing it in the console now, but the changes didn't seem to be reflected in the game. Perhaps this GameSetting is no longer where that information is kept? That would be surprising, but so was this result.

Cipscis

I can confirm that. While other GMSTs do work (iDropWeaponChance for instance (or similar, can't look it up right now)), I couldn't get iInventoryAskQuantityAt to work (changed it from 5 to 3). At least not what I think it should do.
I haven't tested with a new game yet, but other GMST changes (by plugin) take effect right away in existing games, so yep.