I think a simple workaround would be instead of changing the existing billing address create a new one and archive the old one that's way old invoice still reference to old address and could not be select anymore for new invoice  because it's archived   

Hello James Camfield

As per your comment.

Yes,you can create schedule action(automated actions executing python code) .
In python code :
1) Check or find partner's invoice(group by partner_id and created from website).
2) invoice state (not posted,cancel)
3) take latest invoice by in search method order='id desc',limit=1---last one invoice
4) check last invoice Address != older er one invoice

then update invoice address as last invoice address

Thanks & Regards,

Email: odoo@aktivsoftware.com

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