TEMPLATES in pages. (And In all apple apps)

"MOST IMPORTANTLY: templates should be editable. "

Any document can be edited.

Any document can be saved as a template.

1. Create a new document using the template you wish to edit.
2. Edit the new document to the state in which you want the template to be.
3. Save the document as a template.

Done.

Follow-up: You may also find this recent post useful:

DELETING A TEMPLATE FROM PAGES!!! - Apple Community

I've not tested the procedure.

Regards,

Barry

Learn more about templates: https://support.apple.com/guide/pages/use-templates-tan5c52a733c/mac

You have a feedback menu item on the Pages application menu — use it, as no Apple product teams read, nor participate in these fellow user supported and public communities.