The shock has bladder that contians high pressure nitrogen, approx. 150 -175 psi. Just leave it alone until it is time to rebuild the shock. The pressure needs to be releived only when dis-assembling the shock.
The nitrogen filled bladder keeps the shock oil under pressure. This keeps the shock oil from foaming. If you are slighlty off on the the nitrogen pressure, it won't make any difference in how the shock performs, but by checking the pressure with a gauge you are going to lose some nitrogen.