Check into booking these as separate tickets. One outbound in "W" and a separate ticket inbound on "B" or whatever fare class you want.

Sometimes the pricing is such that UA simply adds the two one-ways together to come up with the round trip price. If you book them separately you may pay a few extra dollars in taxes but then you have no issues of change fees, refunds, etc. on the return ticket which is solely governed by the fare rules of the class you purchase.

Note: this does not work all the time and you may find the ticket price goes up significantly. It's worth a shot. It works almost all the time for domestic tickets, less so for international.

Good luck.
-RM