-snip-
As far as I know, the decision can not change. IMO, admin/mod give forgiving for all the mistake that he ever did.
But if the user breaking the rules after he gets unban-approving, I think admin/mod will permanently ban that user without any chance to appeal.
or perhaps an old case of spreading malware, or something like that
In this case, that user should remove/repairing his old post after his appeal approving.
If he didn't it, he will get permaban without appeal opportunity.