A ".38 +P revolver" is simply a .38 Special revolver which is rated to fire +P loads. It's still a .38 Special, and the +P doesn't change the dimensions of the round itself.
Depends on how old the revolver is.
no
1. You will have to call S&W for a correct answer 2. Plus P means higher than normal pressure ammunition. "Other than 38 plus P" could mean another caliber, or normal pressure ammunition. The caliber should always match the revolver you are shooting. Normal pressure ammunition of the proper caliber can always be used in a firearm, unless the firearm is a machine gun which requires higher pressure ammunition to operate consistently.
yes, but not too often in a light weight 38 revolver.
No. This was made long before +P ammo was created.
Yes. Shooting a lot will accelerate wear on the gun, but occasional use is OK.
The mfg. Says yes you can
If you mean can you fire non plus P ammo in a gun rated for plus P, yes, you can safely do that as long as it is the correct caliber.
Contact S&W.
Yes, you can but it is NOT recommended. Only shoot +p ammo in .38SPL guns that are marked as +P.
NO
Not recommended unless the maker says it is OK to do.