Is there a command that i can assign to a button so that i can have different button control rates? 4.65 works great unless im using a really fast car or trying to stop where its bumpy. Driving the lx6 with cold tyres either involves going up a gear or doing a bunch of little burnouts as i try to get gradually on the power (works wayy beter with the slower cars). If i cant change the button control rate then is there a way to assign a button to say 70% acceleration?

no not possible, sorry.

I'm not sure if the LFS Scripting environment allows you to change the button control rate, but Id make a small script that loads when I press a certain button to change it.

Go take a look in the LFS documentation on the matter.

Edit: I think Boosted pretty much answered it :P