Is there a way to remove the 8.3 filename limitation on the SD.h library? I need to be able to create text files on my SD card that are with names longer than 8 characters (which is what the SD.h currently limits me to). A choice would be to move to the SDFat library but before considering that option, is there a way to just remove the limit on the SD.h (because my code already implements the good-old SD.h)? What would be the best way to go about this issue?
The 8.3 "limit" is not a "limit" that can be removed. It is how FAT filesystems work.  Longer filenames are a "fudge" extension overlaid on top of that fileststem structure. To be able to use them you would need to implement that extension.

Simpler to switch to a more modern implementation.  FatFS is your friend:


LFN support, including UTF
Faster device access
More efficient
Can handle more devices than just SD cards
Can handle multiple devices at once


There is an implementation here though I don't know how good it is (I use it on chipKIT where it is bundled by default).

If you can't get FatFs then basically anything is better than the SD library to be brutally honest.