There is no way to reset this on the 922 cartridges.  Once the cartridge registers as 'low' once, it will always register as low, regardless if it has been refilled.

Printboy007 is right, there is a chip on the cart that counts the number of dots printed out. The low ink message is an estimate of when that cartridge should be empty based on the number of inkdots that have been printed to paper. Once the chip reaches that limit then it is forever "low." You should still be able to print with a refilled cart, you just have the annoyance of the low ink message. If you can live with that then use all the refills you want.