And it also doesn't matter if it is before or after the plany has been pollinated.

Except that if you find the plant you want and want to "save" it, it needs to be unpollinated. However, in either case it can still be used to pollinate other plants.

Also, in case people get confused, the seed you see by double-clicking the pot is the original seed the plant grew from. That doesn't change with Mutation.