I've never heard of a mod that
lowers the level cap, but I wouldn't imagine that it would be too hard to create one.
Maybe a script that first checks the player level and once it's equal to the desired level it sets a global to the players current experience points. Once that global is set it checks the players experience against that number and sets it back whenever experience is gained.
Just off the top of my head:
If XPGlobal == 0Set LevelCap to Player.getlevel if LevelCap == MaxLevelGlobal set XPGlobal to Player.getav XP endifelseif XPGlobal > 0 if Player.getav XP > XPGlobal Player.setav XP XPGlobal endifendifend
I suppose you could also make a quest script that upon reaching the desired level it sets all the IXPReward values to 0 and ends the quest, that would propably be more stable but would require more work.