Did anyone ever create a mod for cleric/thieves that fixes how awkwardly using their Thieving abilities? They put it under Special Abilities, which means twice the work to unlock, disarm, and pickpocket. Ever hear of a fix for this?

Why would you want to play a cleric/thief?
It's probably the most useless combination of classes, since the cleric's weapons restrictions means you won't be able to backstab.

You can still backstab with clubs and quarterstaves. Staffs in particular are really excellent backstab weapons, due to how many really good ones there are.

For the original question, I don't know of any way to restructure ANY of the classes' action bars. They appear to be hardcoded. So unfortunately, no, all of the thieving has to be done out of the special abilities... but that's really just because cleric/thieves have too many abilities to all fit on the bar at once. Still, you can hit F12-F1 to access them, which might save some time vs. clicking.

Bevinator is quote right on the staves, there is even a halfway decent club. Besides which, come ToB my character could use any item, if a bladed weapon had enough Thac0 that might compensate for my lack of proficiency. I had toyed with giving him/her Tuigan Bow +1 in ToB, I'd take a hit on Thac0 for sure, but 3 attacks vs 1 with slings? Just contemplating. To be honest, the action bar is probably enough to dissuade me.

Heh, backstabbing with clubs sound silly, but I guess staves is not too far fetched. After all, the strength of staves as weapons is supposed to be their versatility.

Or maybe it's a cultural thing. In Norwegian "to backstab" is "dolke i ryggen" which directly translated is "dagger in the back".

Maybe with clubs it's less backstabbing and more caving their skulls in from behind? Plus as I said, come ToB I could be using Celestial Fury, Blackrazor or Carsomyr if I wanted! lol (though Carsomyr can't BS)

In the US backstabbing doesn't specify the item used, though dagger/knife is probably what most people imagine. In World of Warcraft I think the only weapons you can backstab with are daggers. In BG I think it's less literal.