It seems like there are a couple of issues going on, but there isn't a way to pull out the minimum jump frames from how the rest of the plugin is setup. You can get jumping down to nothing by setting Jump Velocity = 0 and Minimum Jump Height = 0 (jump frames only divides the amount in jump velocity). It still has a frame of jump animation, but if you want to get rid of that the best bet is just to overwrite the jump button entirely.
As for updating the jump physics, they will update but currently you have to wait until the next scene to see the change (because of some interactions between a number of other variables, the game needs to do some error checks when it loads a scene for jumping). I'm planning on adding an event that lets you update the jump fields directly, but I haven't had a chance to create it yet.