This is an improved version of my earlier design, which both extends a toilet paper holder and adds a quick-change feature. It requires both flexible and less-flexible filament. I recommend TPU and PLA.
You have to print one copy of the rigid part mirrored. You might need to adjust the size of the flexible part to match your TP holder, but be careful how you scale it or it won't fit with the other piece anymore. After printing, glue them together with cyanoacrylate.