Couldn't I just turn back uphill and ride for a few minutes? It shouldn't take much time to use up 5% of my battery on such steep hill and regen braking is so inneficient that going down the whole 13 mile hill would probably recharge it less than 5%. Or maybe a more convenient fix would be to splice a high- voltage shutoff to the charger so it only charges to 95%. Even better is to find a bike with motor-braking that can be activated independently of the regen but since Zeros are high-end and even they don't have it I'm doubtful they exist.
AFAIK, all electric motorcycles have adjustable motor regen. Zeros have both, adjustable brake and deceleration regen. Energica only has deceleration regen. None on the brakes, just like Tesla. But they have so much deceleration regen they need no brake regen.
You can set Zeros brake and deceleration regen independently, but I normally see no reason to NOT put the brake regen at 100%. The deceleration regen is more of a personal preference. You can have it set at 100% and then use 0 to 99% by not releasing the throttle all the way. So it's more about what you want the bike to do when you fully release the throttle. It's a good habit to get used to NOT releasing the throttle all the way unless you want to make a full stop.
As long as you're a few percent below 100% SOC you will have full regen. The higher end bikes will have a way to set that so charging stops at any percentage you want. Charging slows down a lot near 100% SOC so it usually isn't too difficult to know when to shut the charging off even when you don't have that feature. In fact, most bikes tell you on the screen how long it takes to charge to 100% with home charging. So if it says two hours and five minutes, disconnect in two hours or less. Use a timer or whatever and get it exact. There are always to prevent a full charge. Zeros have a lot of motor drag even at 0% regen. It coasts poorly no matter what you do, unlike Energica which coasts very well when set for no regen (or set for full regen with 100% SOC).
However, you should charge once in a while to 100% for better battery balancing.
Your big problem is your limited budget--Especially these days when demand for EVs of any type is high because of the ridiculously high gas prices. IMO, EVs are the best vehicles for hills. They don't compare at all to ICE vehicles in the hills.
-Don- Reno, NV