For your #2 question:
In USPSA (American version of IPSC) "Exterior visible mods are the ones very limited. Internal changes not so much.
In IPSC the rules are different in this case, and I don't know how they would enforce them. The hammer is 'visible', but I don't know if it's the same one that justaute linked to. If so, it's good-to-go. Either way, at a local match it's unlikely to come up at all, but You will know .
Where are you going to shoot an "IPSC" match?