Final answer:
The correct term to fill in the blank is 'amend' as the sentence refers to making changes to the old city charter.
Step-by-step explanation:
The correct term to fill in the blank in the sentence is amend. When a city charter is amended, it means that changes or updates are made to the existing charter without completely replacing it. In this case, the sentence suggests that it is too late for amendments and emphasizes the need for a completely new plan.