Just a nice, old fashioned spit and polish tune and properly fitting guides will see a 25mm one shooting oh so sweetly, even at full power, Rhys. No need to de-tune, really, unless you just had the burning desire to do so.
Supposedly, the 26mm versions do benefit from a slight short stroking and piston lightening.
If you were adamant that 8 or 9 is to be your desired output, I have no doubt that a suitable short stroking and matching spring will yield a lovely, super-smooth and benign cycle. A bit like a HW30S with more weight to deaden the already low recoil even more so. This suppressed recoil and learning the trajectory inside out will make for a very usable and accurate gun at Bash ranges.