If it walks like a duck . . .
You can only say it isn’t a modification by being cute. It modifies the referee’s discretion under the Laws. If they said 5 minutes or until the next stoppage, no one would even debate whether it was a modification—itks only because it’s minor that we try to pretend it isn’t. That said, this is no more of a tweak than things like directing referees not to raise the foul bar for PKs. That isn’t consistent with the Laws either. But this kind of guidance tweak has been tolerated by IFB/FIFA--until the decide they don’t like something and advise that it shouldn’t be done. I would imagine they are sitting with this one to see how it goes, and it may be implemented into the magic book if they like the results.