Do Meridian still have access to the original Sooloos program sources?
Of course. It is their IP. Why would they not.
Do they actually have any programmers that work for them who would be capable of understanding/modifying these sources?
No idea but probably yes.
....original programmerS (at Roon?) to make the necessary software change.
I doubt it but who knows. Roon will be busy with Roon stuff.
If the theory is right that Tidal changed their login process, I am surprised that they did so without the courtesy of informing their partners in advance, of which there must be many.
....too many wild assumptions here.
It's odd that some people are impacted and others not. Sounds bizarrely like another proper crisis doesn't it.