Normal roster rules usually apply to isolated COVID IL replacements. COVID IL players don't count against the 40-man, so it's easy enough to add replacements, but you have to DFA/waive those replacements to remove them, just like normal. However, this year, MLB said if a team is dealing with a COVID "outbreak", then those 40-man additions could be subsequently removed from the 40-man without being waived when the COVID IL players were reinstated. They didn't publicly define what constitutes an "outbreak" but I'm guessing the Twins would qualify now, with multiple postponements and players affected. Here's an article from March explaining it a bit: https://www.vivaelbirdos.com/2021/3/31/22359475/reminder-on-2021-mlb-playing-rules-and-covid-protocols Since that article was written, the Nationals apparently qualified as an "outbreak" and did this with one outfielder on their roster, but other individual COVID IL replacements have just been treated normally. Not that I would expect Riddle, Telis, and Farrell to have any trouble clearing waivers!