I am trying to find info on template changes between versions of VM 2.xx but cannot find them.
Can someone please point me in the right direction?
(I want to update from 2.0.26d to 2.6.6 and want to see if my custom templates need some changes)
There were no template changes which is why you cannot find them. There were minor changes in JavaScript which did affect some sites with 3rd party Joomla/VM templates, but nothing major.
To compare changes between versions I suggest you use something like
http://kdiff3.sourceforge.net/ (http://kdiff3.sourceforge.net/)
It is great to see what changes are made no matter how small across the whole set of files
Just download the releases
Unpack them into their own folders
Then compare the folders
You will see all the changed and file variances along with the code highlight of the change for each file