I hate when my 10 years old sister tampers/messes around with my PC.
Might they be used interchangeably in this case?
In the casual sense you are using it, they are more or less interchangeable. In a more formal sense, one might consider tampering to be deliberate (and possibly malicious). "Messing around with" generally has a less formal, more "playing with" feel to it. It is no less annoying to the owner of the PC, however!