The forum can't find your model, I don't know what your rear hub looks like. Bionx is an integrated system, I don't expect you can modify much there.
And I've just experimented with the geared wheel motor market, there is a reason that Luna is always out of stock. The 1000 W 48v one I bought elsewhere lasted 60 miles. There must be a initial quality problem in the $220 versions. It was fully capable of 15% grade with gross weight of 300 lb though (me + 50 lb supplies).
You can change the drive wheel to have more teeth on the lowest sprocket, to lower the gear ratio. In the 11 speed clusters, 11 to 34 tooth range is pretty common. You'll have to match the chain design to the drive spocket. 6-8 speed chains are one width, 9-11 speed chains are thinner. You'll need a custom chain length too. and changing hubs gets on into the custom spoke length market, and no, the spoke calculators on line only get close, not good enough. The bike shop charges $122 to put something custom in an existing rim; I bought 3 different spoke lengths for $63.
As far as strength, I'm age 67 and am able to get that 300 lb up the 15% grades without stopping and without power. Not in May, but usually by mid June. My mountain bike had a 32:28 low ratio, and 26" wheels. Those 15% grades are the reason I bought geared hub motor instead of mid-drive; I can't do without the low ratio front sprocket. I sure as **** couldn't do without it when the battery and wheel failed in the first two trips and I had to pedal more than 10 miles to destination each time. The nice thing about geared hub motor, they don't drag when the motor is dead.
Have fun hot-rodding.
