One issue I have with BG1 is that in order to raise or lower your rep you have to commit either an act of "good" (save the cat) or an act of "evil" (kill the cat). The good guys however also have the more pragmatic option of donating money to a church. Evil PCs, or even neutral ones wishing to decrease their rep, don't have this option.
Sure, there are also quest-related ways to decrease your rep which doesn't involve killing, like scamming the bounty collector in Nashkel. But the point is that evil/neutral PCs still don't have the ability to lower their reputation at will the same way good PCs can raise their reputation by donating gold to a church.
As far as I know, the only other way to decrease your rep other than murdering innocents and finishing quests "the evil way" in BG1 is to invite Drows into your party. This, however, amounts only to a total of -4 rep in BG1:EE.
I propose something very simple: just add a rouge cleric of Talos who runs a little chapel in one of the towns, and whenever you donate the equivalent sum of gold required to raise your rep in another church, your rep decreases for donating to an "evil" church.
If somebody knows an alternative way to decrease your rep that I have missed that does not include console muckery/modding please tell me as I'm looking for ways to keep Edwin in my party