Excel - creating a master template?

Sorry for my second Excel question in as many days! Almost there now though :)

I've created a template for an invoice for my mum... is there anyway I can sort of lock the file, and create sub invoices from it, hopefully achieving...

1. Any changes made to the default/master invoice will reflect on all of the others


2. Locking down the spreadsheet so she can only edit certain columns? :D

Any suggestions would be fantastic, thanks