[Currently]

Cutting a spring will make it stiffer.

Rather than do something to the suspension,
can you pull off the seat and replace the existing foam
with automotive high density foam an inch thick?

You can get it at a junk yard from seat bottoms if you are
strapped for cash.

Personally, I would not mess with suspension components
until you consult with a pro ...

typically with some bikes, you can swap out the dogbones
the shock is attached to. But like everything else, the price
you pay may not be worth it.