Hey JHarris - Sorry to hear about the rescheduling, but I think you're right that getting married on Friday will work out better in the long run (provided your hair/makeup person agrees!). I think it'd be so much easier to arrive on a Thursday for a Friday wedding and stay through the weekend than leave on Wednesday for a Thursday wedding. Maybe it's just me, but getting off work can be tricky at times. I'll keep my fingers crossed for you that the final pieces fall in to place. Also agree with what others said about the Save the Dates - no need to redo, maybe just an email instead? The guests know when the wedding is, another day shouldn't make much difference. Also, if you're planning to send booking info with the invites, you can easily make sure they're aware there.
LisaDSO re the flower petals - I don't think there are any restrictions at the Royal (whether they're real or artificial), though customs may prevent you from bringing real ones into Mexico. The Royal will sell you a bag of petals for $20, I believe - they recommend 5 - 10 to line an aisle runner, and I think someone on here was fine with 5 bags.