Editing Parts Created using split part

I am a newbie, so this might sound stupid. I was wondering if it is
possible to split a part into multiple parts, then create an assembly,
and still be able to modify parts by opening the new part name.

When I open a part that I created using "split part" it only gives a
STOCK<part_name> and doesn't let me change anything.

One thing I would really like to do is just export one of the parts
without any references or anything as a stand alone part, just lock it
the way it is, and export it as a seperate filename, is this possible?

Thank you,
Blisspikle