If I pull a figure in a booster that has the wrong dial, and I print a copy of the dial that it is supposed to have and glue it in, is that cheating?

Technically, it is covered here:
In your case, you simply never owned the original form.

The big issue is that during an event, it is difficult to verify the legitimacy of the printed dial. (IE, "Well, I know this guy has Pulse Wave, but does he really have 5 clicks of it?")

Talk to the judge, though. Some might allow it, though you could still get an ornery opponent denying you.

It isn't so much "cheating" as "hard to police against cheating". If you run it by your judge and he looks it over to make sure it is the right dial and whatnot, he can allow it; but every opponent must also allow it. If this piece is Ventry, Crisis Superman (pick one), Chanos, etc; you will likely be out of luck.

It depends on three things;

1. Your judge.
2. The figure in question and how powerful/broken it is.
3. Your opponent's level of jerkiness.