I don't know if there have been changes to the newer models and maintenance tanks, but this is from the old Wiki back in the days of the iPF6100. Information provided as is, whatever you decide to do is at your own risk:
After digitally flipping though the iPF5000 service manual, I deduced how to reset the maintenance cartridge (called "W-INK" in the manual) usage count for my 6100. For those who wonder, the 6100 will no longer operate once the maintenance cartridge hits 10%. I verified this by reading the W-INK usage counter after the printer insisted on a new maintenance cartridge.
1. Start the printer in service mode
2. Press "Menu". There will be a new entry called "SERVICE MODE" with a different menu structure and navigation system.
3. Familiarize yourself with the following facts while in this menu:
Left and right change the categories.
Down and up go into, and out of (respectively) submenus.
From what I've read, the service mode is very powerful - lots of opportunities to really mess things up. Be careful.
4. Select "Service Mode" as you normally would, i.e. scroll down, then press OK.
5. Press the right arrow until you see "Initialize".
6. Press the down arrow.
7. Press the right arrow until "W-INK" is displayed. (Note: be sure you select "W-INK" from the "Initialize" choices instead of "W-INK - CHG CNT" which sounds like just the thing, but doesn't work.)
8. Press OK.
9. The display should show "=W-INK" for about half a second, then plain "W-INK".
10. Press up until you get back to the main menu. Press information until the maintenance cartridge capacity is displayed.
11. The maintenance cartridge capacity is now 100% (aka empty).
12. Press and hold Power to turn off your printer.
13. Turn it back on normally.
14. Maintenance cartridge capacity (not usage!) should still be at 100%.