As far as I can see, the "file management" system in a digital camera is nowhere near the robust multi-featured system found in a computer. As a result it is very likely a change from the standard IMG_xxxx filename may well be considered a corrupt directory entry and just ignored. Over the years, it has generally been recommended that you not alter the file on a card anywhere but in the camera, and in fact the long time recommendation is to format the empty card in the camera you are using it in. Even switching cards between cameras is at best not a good idea.
In these "modern times" as digital things have become a bit more standardized, it may be possible to get away with more shenanigans outside the camera, but I don't like to count on that. And given that a Gigabyte in today's dollars costs about what a Megabyte cost in 2000, saving memory doesn't seem all that important!