RE: Upgrading to 3.19 kernel with Dell factory 14.04 image
No it is not. Prior to trying this from a factory reset state, I had done it from my system after I had applied the Dell 14.04 backport fixes from this link:
Curiously, when running this after applying the above fixes, wireless will not stop functioning. So it may be worth trying.
Bottom line, if you know what you are doing/understand what is going on (upgrading the kernel in place using the Beta enablement repository) then I see no reason for you to go back to a complete factory reset. I would, however, do a quick backup of important files and things just in case.