I do not think the rules permit an added on trigger stop like a screw in the back of the trigger. I know some Smiths have a factory stop set into the rear of the trigger guard, that would be OK, as would the rod inside the rebound spring as seen mostly on N frames.
You bet, as long as all safety features remain. It was once common to leave the hammer block out of PPC guns and that would not be allowed in IDPA... nor smart.
That would place you in ESR with a power floor of 165000, versus SSR with a power floor of 105000 when using speedloaders.
That is ok but I am sorry I had mine converted. SA is handy to have for testing ammo and to permit rolling the cylinder to check for binding when loading.