No. The receptacle, wiring, and breaker ratings should all be matched properly. Replacing the 50A receptacle with a 30A receptacle isn't a problem, since the wire should be rated at least 50A. But a 30A receptacle should be protected with a 30A double pole breaker. The breaker only costs about $8.00, so why wouldn't you change it given you don't have to change the wire which would actually be expensive or time consuming? The fact that you mention a 50A receptacle protected by a 20A existing breaker isn't normal either. I would check to make sure the wiring is actually rated for 50A and that someone didn't just throw a 50A receptacle onto a 20A circuit. (This means your wiring should be at least #8AWG THHN Copper wire.) If you protected a 30A receptacle with a 20A breaker, the load might trip the breaker often, considering the appliance requiring a 30A receptacle probably requires about 30A. If you do not understand the work well enough to accomplish it yourself properly and safely, don't try it. Consult a professional electrician, as they are proficient enough to do it properly and safely. When working on electrical circuits and equipment, make sure to de-energize the circuit you will be working on. Then test the circuit with a definitive means to make sure it is off (multimeter with metal tipped leads, voltage tester with metal tipped leads, etc., not a non-contact tester, which is non-definitive.)
You will need to unhook the dirt receptacle at the bottom base of the unit. Then, empty the debris into the garbage and replace the receptacle.
To replace breakers in an electrical box it is extremely important the replace the breaker with the same wattage. Do not replace a 100 breaker with a 20 breaker is can cause damage.
ensure all power has been removed from the receptacle lines
No, it would not be safe unless you replace the 20 amp circuit breaker with a 15 amp one. All the components of a circuit must meet the minimum capacity. If you replace a "big" receptacle with a weaker one, it may cause problems.
Yes, but they are easy to replace.
you have to replace them......they are not self resting.
everything improvements to existing technology, inventions that replace existing technology
Remove the existing one, replace it with a new one.
Yes, that would be safe as long as the circuit breaker remains 15 amps. The 20 amp receptacle is more robust (and more expensive) than necessary, but that's OK.
The one you most likely can't find is right on the back of the fuse receptacle. It's a fusible link and requires you to replace the receptacle.