So if I make a copy of my old wallet and mess around with that (import convert etc.) my old copy will still hold my bitcoins right?
Correct.
I mean as long as I dont spend any bitcoins it doesn't matter what I do with the copy right?
Yes,
but make sure you keep every copy safe. To state the obvious: don't use it on an untrusted computer.
(I can delete the copy after I verify the bitcoins?)
Yes, but keep in mind USB-sticks don't last forever. I wouldn't trust just one copy, but keep a few.