short answer: sure why not

longer answer:

it depends on the particular satellite and a lot of stuff like, does it receive firmware updates from the ground? was it designed with ROM chips that have the software and it never does anything except send data? does it encrypt its communications signals?

suppose it were the case that the software running on the satellite had a remotely exploitable vulnerability, yeah it could work; but that requires also that:

(1) the satellite has some kind of software interface which can be used via radio communications

(2) the satellite doesn't encrypt its communications OR the encryption for the satellite has been broken

(3) someone has sufficient knowledge of the software running on the satellite such that they can form an exploit without permanently disabling the actual satellite

spook answer:

my personal theory is that the X-37 is an autonomous craft with satellite-hacking capabilities; maybe that's just "can use its fancy arm to poke it with a soldering iron" or "fly up and attach an implant crafted for a specific satellite" but who knows