Aces,
If you need to seat late arrivals simply seat an extra table. If you have 100 players seat 12 tables of 8 & 9. That will give you the seats you need for them. Then they will be blinded until the buy-in period is over. At that time remove the empty seats chips from the table.
If you just don’t have the tables then place some of their chips in the next pot after they sit in.
As for the re-entry, a freezeout by definition is a one buy-in and out. I’ve seen “freezeouts” with a one rebuy or add-on. Those aren’t freezeouts.
House rules take precedence over all other rules. If you want to allow one re-entry during the first hour, go ahead. Just make your rules and stick to them. If this re-entry is causing an issue with your players find the best compromise and make it the law. No mater what you do you will upset someone.
Hey, it’s your game do what it takes to run a good game that players want to come to.
Good luck,
Martin