I took one of the animations from one group and copy, changed a bit, and saved it as a CastTarget.kf file. Though it keeps saying it is a bow animation group file, and whenever I go into Nifskope and try to change the Bow group thing to Casttarget, it reverts back to bow anyways after it is reloaded. How can I fix it and make it usable as a casttarget animation?

You have to change the File Name, the Active Sequence Name AND the Sequence Tags as the Bow Attack Tag's are completely different from CastTarget Tag's.

I am of course assuming your using the BowAttack.kf animation as you did not specify.