Shouldn't be a problem. Flew my wife over on a 2-way ticket, since it was just slightly more expensive than a 1-way, leaves some room for us to play with later on. Ended up not using the return trip, this was for the initial greencard entry flight.

Had a friend who needed to fly from UK - US one way, and got him to buy a round trip since that priced out to lower than the one-way. UA changed the flight timings by 2 hours for the return trip and he got 1/2 of the ticket refunded back.