With the clutch in the engage position.....is the clutch only able to tighten the belts or is the clutch able to move in either direction as required to maintain tension?
The former.
Why would why would changing the fuse make any difference?
The fuse is rated substantially less than the circuit breaker that protects the clutch circuit. The fuse will blow before the CB pops. That way a motor problem will blow the fuse but the warning light will
stay on. If one just relied on the circuit breaker (and no fuse were in the circuit) then an overload problem would trip the CB thereby preventing the correct level of tension in the belts and simultaneously extinguishing the warning light - not a good thing. If the fuse blows it
might have just been because the fuse has got old and tired or a short duration transient caused the fuse to blow. In these circumstances changing the fuse will get you back in the air again. That's why a spare fuse is provided. It's happened to me once, I discussed by phone with the duty engineer. Changing the fuse on his advice got me back to base (and ultimately to the pub).