Wooglin

I have currently booked for next week:

CLE-SFO-LAS in XN for 12.5K
and the return 2 days later
LAS-LAX-CLE in YN for 25K

on a single PNR

I'm tempted to cancel the return and take F9's nonstop LAS-CLE as part of their 2-day $19 sale.

I understand (I think) from reading the UA website that canceling for redeposit would be $75 as UA Gold.

Can I cancel only the return segments before the start of the trip? Would I still have to pay the entire $75 to redeposit only the return segments?

Can I cancel the return segments after I land in LAS, but before check-in on the return? Would there be any benefit in doing so?