For driving a set of LEDs from a 3.3 or 5V logic-level uC signal you *should* be fine. Just keep in mind that because the TIP120 is a Darlington pair transistor, it has a Vbe forward voltage of 1.4V rather than the 2N2222's 0.7V, and may have a higher gain than the 2N2222, so be sure that you are properly limiting the current to the LEDs if you weren't already doing so.
It's not a 1:1 replacement per se, so depending on the configuration there may or may not be issues. We would probably need to see a schematic to be sure.