You should never use the RMAN COPY command because it was deprecated in 10g, as I said before. It is an old syntax that Oracle don't want you to use. In a future version it will probably be removed completely. That is what deprecated means.
Imagine COPY never existed and you only copied files using BACKUP AS COPY... They do the same thing, but one is a deprecated syntax.
BACKUP AS COPY is nothing to do with a restore. It is a backup operation. You can use it to move files from ASM to a filesystem, or a filesystem to ASM as follows.
- Use BACKUP AS COPY to create a new copy of the file in the new location.
- SWITCH to use the new file.
- Recover the copy (if necessary).
- Get rid of the original file, unless you are keeping it as a backup.