generally a fair bit of r&d has gone into getting your fin to perform the way it does. As a rule i try not to change the leading edge or foil of a fin and will only do work to remove damage to the fin.
I wouldn't recommend dulling the lead edge if you want to maintain performance.

The leading edge of a fin shouldn't be sharp! I'd guess even the fin slowy did 50kts on didn't have a sharp leading edge.
There needs to be some sort of radius there, about .25mm perhaps, depending on the foil shape.
Part of a foil description is the leading edge radius, if you can figure out what your foil is, (or the closest thing to it) there are tables online giving leading edge radius.
A sharp leading edge is only good at 0 deg angle of attack, (dead downwind), but you'll probably never use your fin like that. The more angle of attack you use this fin at the more the leading edge will want to stall.

I think you can use 100 grit first then finish off with 400/600, don't make it too blunt though, that can slow you down, just so you don't cut yourself should be fine.

The trailing edge can benefit from being sharp, but making it .5mm square doesn't loose much performance, and is a lot safer.

Never been got by a standard fin as yet, but a whole different story with weed-free fins.

Too many cuts and nicks to think about from them over the years. problem is usually when water starting or getting out of water or lifting board up by the back strap and copping it right into the shin.

I agree that the trailing edge could be dulled a little with minimal performance loss. Plus the benefit (hopefully) of no blood in the water while sailing. Who wants to stop sailing just because of a little blood?

Funnily enough a flat trailing edge will affect the drag more than a sharp leading edge.

Ever wondered why plane wings have a big round front nose but a very long sharp trailing edge.

The trailing edge gradient will determine the pressure drag coefficient