You have a template which contains the tag '__project-number__' For the tag the feature 'Reuse Replacement' is activated
First you instantiate the template, the replacement dialog pops up and you can replace '__project-nr__' with '123456'
This creates a new page. Next you use instantiate the template again and use the new page as a target.
Now in the replacement dialog, the project number tag will be prefilled with '123456' or not appear at all.