I have definitely had negative RDM credited from Chase in months where my refunds were greater than my purchases. There has been speculation (but I believe no evidence) in other threads about whether they would do this with EQM credited before Jan 1 and refunded after Jan 1.

A variation on the refundable "trick" is to buy the outbound in the cheapo class you want and put the return in a refundable bucket. You can subsequently change the return with no fee *and* without regard to advance purchase requirements. If you are trying to change the first leg you must meet any advance purchase requirements on the new fare.

In addition, on most fares the rule is that if the first segment is unchanged, then the price you get at change time is the price at *booking time*, not the current price. However, I've found the fare desk agents to be as variable as the reservation agents, so it may take a few calls to get things to work out.