They probably won't let you put explosives in there. I'm sure it takes quite a bit more talent than most amateurs have to make a rocket with fuel that is safe to put aboard another rocket.

Just imagine if it'd ignite or blow up mid-flight. It'd be fatal for the whole mission.

Yes. There's not nearly enough capacity on one of those tubesats for a workable propulsion system and any kind of payload.

A lot of the cost advantages of the tubesats (which, incidentally, have never been launched) come from their standard design.

You don't really have room for any type of chemical engine in something this size. Typically satellites this size actually use tiny motors and electromagnets which interact with the Earth's magnetic field to orient themselves.