Actually, I'm not sure how that would work. The UCMJ is a system of laws enacted by Congress...Obama can't change that. I suspect he could issue an EO prohibiting enforcement of specific articles, but that would be an even bigger and more contentious political bombshell.
Disagree, while the USMJ is written by congress, Executive Orders have and historically have been used to change policy and require zero congressional involvement. The most famous at least publicly is the end of segregation in the military.
If Fauxbama was serious about this whole issue, he could issue executive order and be done with it. He won’t of course because he’s not interested in actually doing anything just telling others what to do while remaining plausible deniability for himself.