Yes you can, not a problem....
it is a viable tuning option that has been in use for quite some time. I used to have a old Zocch Z3 dual coil that I ran one Xheavy and one Heavy spring it to get it just right. Two X's were too stiff and two Heavies were too light. The Xheavy/Heavy combo was perfect. You should have 0 problems runing the heavy/medium combo. It is NOT recommended that you run any more than a one rate difference between sides though. In other words an Xheavy/medium or a heavy/light would not be a good thing. No worries though, what you want to try is perfectly fine. It is a nice thing to know too, as it doubles your tuning options for dual coil forks. So have at it. Hopefully it'll dial you in.:thumbsup:
Good Dirt