The alternator is grounded through the case, so additional contact will not create an electrical problem. This is why there isn't a big black wire connected to the alternator alongside the big red wire.

The outside of the head should not get appreciably hotter than the coolant, so that is not a problem.

I read into your question that nothing else was changed except for the A/C install and the new bracket came with the kit. That tells me the new bracket moved the alternator closer to the cylinder head. This could mean your pulleys aren't aligned any more. That is a problem.

You may be able to use a longer belt if the alternator bracket has enough adjustment to move alternator away from engine.

R.