Nothing you can do from the outside will blow that fuse.
Let me amend that: except for the speaker jacks, nothing you connect to the jacks will hurt the amp.
Overdrive pedals distort the sound, that is all they do. Distortion can't hurt the tubes or the resistors or anything else. If your external device has too strong a signal, then it will distort the amp. If it has too weak a signal, then it won;t be very loud.
USUALLY effects with gain are better in front of the amp, while time related things (reverb, delay, chorus) are better in the loop. But that is about how it SOUNDS, nothing to do with safety. And if you connect it up in a non-usual manner, if you like the resulting sound, then it is OK.
Now before someone brings it up... Yes, if you take the output of some other amp, and instead of conecting it to a speaker, you plug it into the FX return of a different amp, it might hurt something. But the speaker output of some other amp is not usually considered an "effect."