Just dropping back to let you know @seffect I tried this and it does work - thank god! I just renamed it by putting a couple of xx’s in front of the envira-gallery.php
But what’s really cool as well is that you inadvertently gave me an idea that will save me so much time with the job I have ahead - it will be much easier to add my 186 galleries from shortcodes than from Cornerstone’s dropdown anyway.
Result! Thank you again.