I wouldn’t think so. Pardons are for crimes that someone has been convicted of, not affirmative creation of new status.
So, he might be able to pardon illegals of their immigration transactions and clean their records, but they still wouldn’t be citizens. (Let’s leave aside the fact that for many practical purposes except voting, they’re treated better than citizens.)
However, a mass pardon might create a major reaction and constitutional crisis. Unless the country is completely lost, it would make election life very hard for Democrats. But, then again, Presidential pardons are last day affairs, the next election is a couple of years away, and memories are disturbingly short.
The reaction to all of this is going to be enormous!