You would have to CPYSPLF to a database file, then rebuild the spooled file from the database file. Unfirtunately, you can’t just CPYSPLF from one to another.
You could try sending the spooled file to yourself using SNDNETSPLF (option 1 from the WRKSPLF screen). Then you could change one of your spooled files to another OUTQ.
SNDTCPSPLF can send to the same system and name the outq to put the copy on.