Is it a good idea to do programs other UC's offer if I'm focused on getting into a particular UC?

If I put time into other UC programs that are my backups, should I mention in my application or will the other UCs not consider it too much? For example, getting involved in a UCSD transfer program but wanting to go to UCLA. But of course I’ll also be involved in UCLA’s TAP or CCCP.

Sure try as many as you want and you should because UCLA is no guarantee.