Greg, I modified a Pure Energy reg on my 48cu.in. Carbon Fiber tank. I originally bought an aluminum tank but it was way too heavy!! I'm probably going to add another 68 cu.in. CF tank as well shortly.
I bought a $25 High Pressure spring pack that changes a 400 psi output reg to 800 psi output. There is a low pressure spring pack and you don't want to buy this one.
You have to completely drain the tank of all air and take the regulator apart. Add one of the Belleville washers from the spring pack to the stack to increase the pressure. This pack was designed to replace the old stack of washers but assuming you already have 800-850 psi then just add one washer following the orentation of the other washers. You will also have to change the burst disc from 900 psi to 1500 psi on the output side or you'll blow the disk as you fill the tank like I did. There is nothing as startling as blowing a burst disk in the car while driving or at home while filling your tanks. There is very little info on this and dealers will not want you to do this for liability reasons. They won't sell you the parts if they know you are going to increase the pressure over 900 psi. Remember, DO THIS AT YOUR OWN RISK.
Here are two helpful manuals to guide you through this.
http://www.buypmi.com/pdf/pressure_springpack.pdf
http://www.buypmi.com/pdf/PE_manual.pdf
