You should try the forums at
www.teambg.com Anyways, here is how I would go about doing that.
1. Open up shadowkeeper and get the exact spell file that is being used.
2. Open up that spell in IEEP and check to see what .cre (creature file) is being summoned when the spell is cast.
3. Open up that .cre in shadowkeeper and check to see the .itm filename that it is using for a sword.
4. Open that sword in IEEP change its "enchanted to hit" value (which is separate from thaco bonus) and then save that file under a different name. e.g. put your initials in front of it.
5. Go back to shadowkeeper and change the old sword on that .cre to the new sword you just made. save the cre.
There you go.
p.s. don't have shadowkeeper and IEEP open at the same time.