Just another comment. If you start with 100 and make the changes then change the post to 250 I would leave the members alone under 250 and not try to take them out of the group.
If you reduce the number to 75 you just start another headache that you missed some members that need to be manually added to the group. Unless you wait for them to make another post in another forum. So the script does its own thing.
So I would start with the lowest number. Move the members and just raise it a little at a time.
Just my 2 cents
