Yeah, there should be no problem taking the reins domestically. Alan Shearer among other is a precedent for the Premier League allowing that to happen. There was another coach to that was given a grace period to complete his badges. I think normally the limit is 12 weeks.
UEFA tend to be stricter. They've given out touchline bans in the past, including for Dundalks manager who was the one I was thinking of earlier. He was banned from having any function for a
few europa league games. (also banned for Molde game)
Anywho, we'll see what happens. Not sure why Blanc would want the interim job unless he think it will become permanent, but he is struggling at his current club.
If it need be, we have other people at the club with a pro license if UEFA decides to be difficult. Think Carrick should have his by now, and that new set-piece coach is the youngest brit to ever acquire a Pro License apparently.