Simply having the mercury enter the bloodstream isn't enough. It will probably end up redistributed instead of eliminated. That means a chelator would be necessary.
If you are going to use the Cutler Protocol, it's usually better to wait at least a few days after replacement to begin chelating with DMSA. Wait 3 months before using ALA.
I never used activated charcoal, so I don't feel confident to give advice about it. I did rinse my mouth with chlorella immediately before and after replacement. The idea is for the Chlorella to attach itself to mercury in a person's mouth, so they can spit it out. I'm not completely sure how much help it was. It didn't hurt.
You are right about not taking Vitamin C before surgery.