Regarding #1, discounted round-trips can be almost the same price as one-ways; if you ask for a change to a one-way, your refund will be reduced by any change fee plus the cost of the one-way. So you should call and ask, but don't get your hopes up about getting much money back.

Re #2, again, the cost of the change may be high. In addition to any change fee, you have to pay the currently available fare for the new flight, which could be higher if your deep-discount fare is no longer available.
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