You'll just end up with a little more glycerin in your soap, but not enough to cause problems, I don't think. I often add extra glycerin to my CP along with my colorants (I use it to disperse my powdered colorants) without any problem.
I don't believe you'll get any scent from the vanilla extract, though. Many before you have tried with no luck. The scent just disappears into nothingness, unfortunately. For a vanilla scent that sticks around in CP, I would use an actual fragrance oil instead.