I tried doing a search on this but couldn't find anything (unless I was looking for the wrong items!).

I want to book a trip to LV but for multiple reasons want to take CO on the outbound and return on America West. When I price a one way on CO it prices more expensive than picking that same CO outbound flight and an arbitrary return flight.

What happens if I book it as a round trip and do not take the return? Can I call and cancel the return and apply that amount plus a change fee towards a new ticket?? Do I have to use it towards the same route (LAS-EWR)?

Thanks.