It looks as if my earlier reply went off into space - the only part that remained was my “tag” under your posting; I’ll try again.
While using a pump, I can’t imagine why on earth you might want to have a pen with either NPH or Regular; your pump basal rates [good pumps allow you to set different rates for as many as 9 timeframes during the day] making NPH or any other “background” insulin unnecessary, and the pump will calculate and deliver a meal or correction bolus based on your carb ratios and the carb count you enter. Virtually error free and a pump can be very discrete. I agree that a pen might be useful for correction bolus if you suspect that your pump might be malfunctioning.
That said, there are ways to do what you are thinking with pens but I don’t really recommend. I started using pens and evaluated new models in the 1970’s long before these “newfangled” prefilled pens existed. In those days insulin came in the traditional 1,000 unit vials [that is after the standard became U-100 and U-40 and U-80 were phased out] and in 3 mil and 6 mil cartridges. The procedure was inserting a cartridge in a permanent reusable pen and screw on a needle every time insulin was needed. Those cartridges could be refilled although it wasn’t recommended.
I haven’t used a pen since the day I started pumping and I hope I never need to go back. I think I still have a couple of those pens about, including the last one I used that included a BG meter and displayed the time elapsed since the last injection - took some of the “did I or didn’t I” guess work out of wondering if I took a shot at the restaurant.