It seems they're unlikely to change mid-season. I looked into the Position Eligibility tab under Players -> Roster Changes and there is no set # of games started/played like we have in the baseball league. This is probably because the NBA has shifted towards positionless basketball and if it's often hard to say which player is playing which position, and when. For example, the Raptors have a lineup with both Lowry and FVV on the floor. They're both PGs, but obviously they can't both be on-ball at the same time. By traditional paradigms, one of them is playing shooting guard in that scenario... So should they both have PG and SG eligibility? Maybe! Maybe we should just have G/F/C, but that seems boringly reductive. On top of that, the ways in which we have classically defined certain positions -- by height and specific skillsets -- have largely fallen by the wayside. Now we have 6'10 point guards who can't shoot and 6'9 centers with no post-up game, and everything in between.
That said, positional eligibility isn't as important here as it is in baseball because NBA players only have 2-4 games per week, so you aren't going to have many situations where you need to bench any of your best players, even if you have multiple overlaps at one position.