I don't think there is.
What I would do:
Open the new template and add lots of Guides to the first page.
Clone the page for as many pages in the required site.
Change the page style as needed and clone this too.
In the original, ensure as many of the colours are set up as themes.
Copy across these objects individually and accept the change to the intended theme colours (having matched names).
Copy a single NavBar instance across (all page names need to match).
Set up repeat on all pages.
Given all major images as Names (filename=imagenn).
Work through Layers on each page (these usually only have content and not structure so should be quick).
Position all elements to the Guides.
Try a dry run to avoid all the little changes where things are just off.
Prove the site works.
Only then add new features (never mix migration from new detail).
I have tried changing a website to a template in situ and that is much harder.
Acorn
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