Howdy
As several have said, it would be helpful if you stated exactly which model Cimarron revolver you have. The revolvers patterned after the Colt Single Action Army are chambered for 357 Magnum, as well as a couple of other calibers. Any 357 Magnum revolver can be safely fired with standard SAAMI spec 357 Magnum ammunition, Italy's proofing standards are tougher than the US standards. So any Cimarron revolver chambered for 357 Magnum, whether made by Uberti or Pietta, can safely fire 38 Special +P ammunition.
The revolvers I see on Cimarron's website that are specifically chambered for 38 Special, and not 357 Magnum, are their Remington 1858 Conversion Model, and the 1872 Open Top. The Open Top is chambered for 38 Special, not 357 Magnum. I suspect that the open top construction of the Open Top makes chambering it for 357 Magnum a bad idea. I suspect the removable barrel held in place with a wedge is not a good candidate for the powerful recoil of the 357 Magnum cartridge. The 1858 Conversion Model has a top strap and the barrel is screwed into the frame. I don't know why it is only chambered for 38 Special, and not 357 Magnum. Perhaps it was felt by the manufacturer that this frame would also not be a good candidate for the 357 Magnum cartridge.
So, it would help if you told us exactly which model you have.
For what it's worth, SAAMI Max pressure data for 38 Special is 17,000 psi. For 38 Special +P it is 20,000 psi. Compare that to the Max pressure for 357 Magnum, which is 35,000 psi.
Personally, I don't see the need for 38 Special +P ammo in a single action revolver chambered for 38 Special, but I doubt if a few rounds would hurt it.