I think the first step is to price the change now so you know whether it causes the fare to increase, and if so, how much. If it's no increase or nominal, then just go ahead and do it. If it's really expensive, then consider the other options (ask for a waiver or wait until you've flown the outbound.

Note that the best way to get the new fare is to do a clean dummy booking on the website. Using the "change flights" function may not return the best fare.