Oliver is indeed right. But it is a bit tricky for Intercont as they don´t sell one ways (except for C and A class). This means you may construct a r/t trip with the outbound being fully flexible (such as YFLEX or DFLEX) but you will still have restrictions on that leg if the homebound has a saturday/minimum number of nights rule. Meaning you can not change the outbound to skip saturday night as that would violate the fare rule of the homebound leg.
So, there is a situation where the "other" fare rule affects the first one and you will not be able to change date of your DFLEX even if availability is right there.
This does not apply to intra european travel as those fares are technically one ways and don´t have any minimum stay or saturday/sunday rules in them.