When allowed to, air will very quickly pressurize an entire system at the same level. Meaning if you use a solenoid to let air from a reservoir flow into a pneumatic cylinder, the entire system will almost instantly become evenly pressurized. If the reservoir started at 100 psi, the system after opening the solenoid valve would have a uniform pressure of almost 100 psi. (it’s less than 100 because the same quantity of air is now occupying more volume, resulting is lower air pressure). If you want to control how much air pressure a cylinder can receive, you can use a pressure regulator. See this article for more information on how a pneumatic system works in vrc
You’ll pump up your air tank(s) to 100 psi. When you open your solenoid, air will flow into your pneumatic cylinder. When you release your solenoid, that air will be exhausted. Each time you cycle your air cylinder from extended to retracted, your pressure will drop a bit. If you want to use less pressure to actuate your air cylinders, then you can install the pressure regulator between the air tank(s) and solenoid(s) to reduce how much pressure is applied, which will make your air supply last longer.
You are correct that the regulator is not programmable. As for pressure, there will be a drop in air pressure every time the air cylinder Cycles. For one single acting air cylinder, you might expect 25 actuations and your pressure will have dropped to about 50 psi by then. Additionally, if you do not use a regulator, the force exerted by the air cylinder will drop as the air pressure in your system drops. If you do use a regulator, set to perhaps 50 psi, your air cylinder will have a consistent Force for 20 or more actuations, although it will be a little less. You could plan on about 6 lb of force at 50 psi. The little air cylinders put out about 12 lb of force at 100 PSI