Because of the unique nature of the 2020 season, we keep learning a little more each day about the rules under which teams will be operating. The most recent of those, at least for me, is that only players from the 60-man roster can be traded. We had heard earlier that players who were removed from the 60-man could not be placed back on in order to make an appearance at the MLB level, though that doesn’t mean rosters are locked.
Players can still be shuffled on and off the roster just like before, so transactions will still take place in more or less the same way they have before.