When you rest your foot on the brake, you put a strong brake on all four wheels through the hydraulic.

When you pull the E-brake, you put the brake on the rear wheels only through the pull of wire.

I don't see any chance you will damage anything. Even if you slow down the car using only the E-brake, you are just heat up the rear brake quickly, which won't do any harm unless you do it very offen at high speed.