I hope you're doing great today, @chochisea.
You can always change the invoice number of your transaction at your most convenient time. Modifying the invoice number will not vary if it's made before or after closing the books.
That said, I'm sharing here the resources about changing the invoice number on sales forms as well as closing your books for reference:
You are always welcome to visit the Community if you have any other concerns. I'll be around to help you out. Thanks for coming, and stay safe.