Making Bike Slower?

[pumpngo]

I know it's reverse to the usual question. I bought my elderly father a trycycle 250w hub motor 48v lead acid type batteries.
He finds it too fast, yeah i know i told him to be more gentle but he's incapable , he used to drive his car the same .
So i'm looking at two options so far , but im happy if they are wrong and i'll go another way .
Option 1 cut voltage to 12v and hope he can go up hills
option 2 put a fixed resistor on signal wire from throttle control
other thing i was thinking but have no idea how to implement is changing the resistive wire that limits the amperage draw. I think it may not work to cap top speed though, but it would slow acceleration.
Any help is appreciated as this is his only transport now, I'm getting his mobility scooter fixed but it has a problem that comes and goes so it's not reliable but also hard to find.

[Tommycat]

With the throttle control option I'd just recommend using a variable potentiometer to at least dial in the resistance when finding the speed you want...changing resistors hunting for the right size can be frustrating. Or just leave the pot it in...
Do you have a programmable controller with the means to do so? Along this line, reading your post perhaps this is what you mean by changing resistive wire?

Regards,
T.C.