Why not just buy a Bisley model gun right out of the gate? Each style of hammer spur was designed to work best with each grip shape. The hog-leg would seem to be best with a long hammer spur that stays within reach when the gun twists through your grip in recoil and allows the shooter to hook his thumb over it, cocking the action when he brings the barrel back to the target, where as the straighter Bisley grip is better with a shorter-lower hammer spur as this grip takes the recoil straight back and does not move in the shooters grip. I would urge you to try each gun before you begin to make any dramatic changes to either.
To answer your question though, both the hammer and trigger are pinned to the cylinder frame of the gun, so regardless of which style of grip frame the gun has, the relationship between the hammer and trigger does not change. Therefore swapping one style of hammer for another should not change anything internally or require any other changes or modifications. What I do not know however is if a Bisley hammer and a Bisley trigger must be matched to one another, preventing a Bisley hammer from being used with a hog-leg trigger. I'll attempt to find out. Additionally, there are plenty of complaints from folks who have sent their 3 screw guns in to the Canadian warranty depot to be converted to the transfer bar system. This suggests that for best results some precise fitting is required, rather than simple parts replacement.
