Not if its not designed that way.
It has to be electric (AEG).
No. Spring must be cocked before each shot.
You kan make 1
There are too many types: airguns that are used in the auto industry, Air Rifles, Air pistols, Air soft guns.
You need both.
Yes it is possible
No, only with a few Marui selected models, or with airsoft guns that have a threaded barrel of the same size.
No. it has to be cocked each time.
No. Wrong size.
new spring or check your compression.
A spring, an electric motor or by compressed gas.
No, not if it's designed to do so.