pinholeprinted Not all spools are empty in the center, which is why I designed them this way. It sounds as though your camera is putting pressure on the spool ends. Because the ends are split, making them longer will not help with strength. I would suggest getting the metal ones instead - https://www.shapeways.com/product/PJBPR6E82/metal-35mm-film-to-120-spool-adapter - they are much stronger.
pinholeprinted I am not completely clear on what you are asking. Most, if not all, 120 cameras do not have the capability to reverse the film, hence, you wind out of a 35mm cassette (with 120 adapters) onto this spool and change in a bag. Since you mention reversed spool and avoiding changing, I assume you mean using an empty 35mm cartridge on the other side (upside down) and winding the film back into it?
I have not tried this scenario but as the film is centered on the 120 format, you should be able to do this with adapters on both sides (not using the takeup spool).