My BGT seems to have removed the XP cap anyway (I'm not sure where else this could have come from -- all I had was BGT and the Fixpack -- not the Tweakpack, which is the one that allows you to remove the cap).

But anyway, while installing such a mod wouldn't create a game-breaking bug, I feel like it breaks the game in the sense of making it too easy. My party without the cap felt overpowered for parts of the game, and I often found myself wishing for more of a challenge. But then there's the parts that are absurdly hard regardless, like Sarevok and Draconis and Amelyssan, and it's hard to imagine having ever been able to beat them with a less powerful party, even with clever strategizing and some metagaming (and without glitch exploitation). Difficulty balance is weird in this series.