In Florida is it possible for the custodial parent to sign off from receiving child support? If so how/where?

You don't have to enforce the payment if you want. But why would you?

Unless it has previousy been turned over to child support enforcement, or collected though the courts, the one parent can merely not "ask" for any, BUT, BUT<<<<< in a few years the parent can easily change their mind, claim in court that the other person has just failed to pay, that parent gets all that back support to pay.

Remember it is not for the parent, it is for the welfare of the child, only the court can change the order, and it will not allow the other parent not to pay officially

If there is court ordered support, then any modificiation to the support agreement must be approved by the court.