To easily reduce the power of the G&G G96, just use a lower power gas, or use
Falcon limiters.
The G96 is basically a extremely upgraded Tanaka M700 AICS. As a matter of fact, G&G was making upgrades for the Tanaka for some years, and then decided to release his own gun using all of them.
So it has great seals, steel bolt and cocking pieces, and overall better quality than pretty much any other airsoft basr you can ever find.
But that also means it inherited Tanaka's crappy hop up design, and to further complicate things, you cannot just simply install an aftermarket conversion chamber and use VSR style buckings and inner barrels like you would on Tanaka's (or KJW), because the nozzle being 1 piece with the bolt in the G&G.
Aftermarket conversion chambers require the longer nozzle they include in the kit to work properly. So you have to either get your bolt to a machinist that will cut the nozzle, drill it and thread it for the conversion chamber's nozzle, or make do with the stock, traditional Tanaka design..
The easiest way out is to use
Falcon's hop rubber in the stock chamber. Should be good enough, yet nothing too impressive. As for the inner barrels, afaik only PDI used to make some for the Tanaka style, but they have been discontinued a long time ago.