If a new resident moves to a locked down memory care unit based on his mini mental and dx, how hard is it to move over to the AL side?

Speak to the administration about this. Each ALF/MC facility has its own rules and its own requirements. Only they can answer this. They will fully explain the expectations of ALF life and the levels of care (usually four) that have to be minimally maintained to remain in said care.

Might be quite difficult to get them into just ALF. Dad was high functioning when he had to be placed. He hated it of course. He got out to the street with a sign for a ride back home. He was immediately placed in a locked unit. It was for his own safety and to protect the home's liability. He declined fairly rapidly there. Had a fall and, subsequently a seizure. I had a durable POA. They called me the FOLLOWING day after leaving him in a wheelchair in the hallway watching him have seizures. Since the seizure was new, after the fall, with them admitting he hit his head I instructed them to call 911 and have him checked out.

My brother went to the facility and tried to see how hard it really was to "slip" in the bathroom. He tried with shoes, stocking feet, and barefoot. No way. I filed a complaint with the state to no avail. Of course, the facility changed names about 4 times in the short period Dad was there.

It turned out to have been a blessing in disguise as my brother was able to get him into another facility closer to home. His brother was able to visit him then. As well, he knew a number of the other residents. He did fine there but continued with seizures until his passing. This facility wasn't a lockdown, and he never tried to "escape".

Patients don’t move out of memory care. If you think he was placed in memory care wrongly then I would take it up with the facility but quite frankly I would probably find another facility better suited for him. Some AL will put up with some degree of dementia and others will not. It depends on a lot of factors. Why do you feel he was wrongly placed? Do you think the doctor had the wrong diagnosis? Maybe get a second opinion on that then.

If the resident was capable of living in AL, they'd have been placed there initially instead of memory care. Dementia does not improve, so the likelihood of moving to AL is very slim.

If someone needs memory care, they're past assisted living level of care.

It is entirely up to the facility itself. So ask them.
ALF and MC are private institutions privately owned and privately run. Because most of them don't accept government funds they are not run with rules instituted by federal and state for nursing homes.

Check with the admins. Generally there are far too many people allowed to stay in ALF who need a higher level of care. They are not staffed in ALF to give the amount of care needed. It doesn't work for other residents. But your own facility may have some sort of "in between cottage" a locked cottage that is providing care and staffing somewhere between ALF and MC. Do ask the admins at your earliest convenience. They generally have rpinted up manuals of their levels of care.