The paint on the disk will be removed once the car is driven about 200m and brakes applied.
Nothing is going to happen to friction. Even a slight pressure applied by the pads on the disk is enough to peel off the paint.
@ Poster
Doing DIY's is a positive thing. But I am afraid you opted for the wrong choice of paint and definitely wrong method of application. Generally callipers are painted either completely separate from the rest of braking system. Or atleast removed and supported (without much stress on brake line). The piston is covered completely with masking tape along with portion of rubber brake line. First you apply base coat and then multiple coats of paint after each layer dries off.
Even then, the paint is not heat resistant enough to sustain under high temperature.
On domestic vehicles, the only portion that requires paint for aesthetic neatness and simplicity is the following two areas on the hub
When you contain the rust that generally increases after each car wash or rainfall, you Rims look elegant. Simple
Your method is the one commonly used by Tyre/Rim shops these days. To earn a couple of bucks, they can lure you to agree what they claim as (Gardi ka Show Ban Gaya). The spray can paint is going to chip off after a couple of runs in stop and go traffic.
