I have managed to solve my problem...
I created a test-bed, online, sub-domain that was not associated with the CDN Cache. A simple PHP webpage with a .htaccess file was used and I was able to experiment and not panic. I do not enjoy having to firefight/resurrect the site (with generated cache) in order to... "Where would you like to go today":)
Testing revealed the conflict was due to <ifModule mod_expires.c>. Localhost threw a wobbler if the statement block did not surround ExpiresActive on, etc
Mission accomplished and now have a single .htaccess file that I can use safely for the Localhost and Online
I did look at your comprehensive online Code Generator and associated links but was unable to find a solution to my problem. Maybe you could add a section on testing or surrounding new code in switchable blocks to facilitate .htaccess upgrades.
Many thanks for your help,