it isn't difficult to photoshop heads onto bodies
That's true, I've done that myself for photomanips, it depends on what and how many photos you have available though. I had a quick look at photos posted by Velund. The first photo (in the phone) - it doesn't look like it's him. The second photo - the guy is wearing a balaclava, so it's hard to say if it's him or not. Third photo - it looks like him, but he's the only one wearing something around his neck - it could be used to hide photomanipulation. The last photo - again, he's the only one wearing a balaclava. Additionaly, there's something wrong with that balaclava and the area on the right of his neck and head looks a bit fishy - it doesn't fit any of the cars, so it could mean sloppy photomanipulation. I'm using my phone now, so I would have to have a closer look later on my computer (preferebly with high resolution photos).
I've also noticed that he's the only one wearing yellow goggles. The soldiers are all wearing the same goggles.
Since Protasevich was working for a year as a journalist in Ukraine, it's possible he simply accompanied the Azov Battalion, as war correspondents often do. The founder of the Azov Battalion stated that Protasevich "fought" against the occupation of Ukraine with Azov
and other units, but as a journalist he was doing it with words, not with a gun. That would mean he wasn't a soldier in the Azov Battalion or any other Ukrainian unit:
en.m.wikipedia.org/wiki/Roman_Protasevich
Those are my conclusions for now.