Will interest rate go up if i cancel extended warranty?

[txprsn]

I bought a Yaris and decided that the extended warranty doesnt really cover much. I want to cancel it but Im concerned that the interest rates will go up. When we were signing the paperwork I was told by the finance person at the dealer that if I didnt get the warranty that my interest would increase by 1.4% and thus my monthly payment would almost be the same as if I had the warranty.

Can they increase the interest rate after signing the contract with a specific interest rate?