Although you can't earn miles and status in two programs for the same flight, isn't there a way that you can earn miles and status in one program while using the elite benefits you've already earned in another program?

(In other words, if you're a 1P with UA but you want to earn miles in M&M, there's a way to enter both numbers in your UA profile so that you can get access to E+ while earning the points in M&M.)

As I recall, there are two fields in the reservation (something like FFA and FFB) that allow this to happen, but most agents are either unaware of how to do so or unwilling to do so.

Big Disclaimer: I'm pulling this half-baked snippet of kinda-information from the far recesses of my mind, so there's a real good chance that it's outdated or just plain wrong.