I asked the same question & Novak's response is below in bold. BL & Brushed are the opposite when you want more/less power (can vs. armature (rotor)).
The “winds” in a BL motor are in the can. They make up whats called the “stator”. The Rotor, is the armature. It’s the magnet and the shaft that sticks out. Changing rotors has an effect on power, but not like changing winds does.
I think basically in comes down to:
-Changing the armature in brushed is where the power comes from because that's where the winds are. A can is a can for the most part.
-Changing the can for BL is where the winds are so that's what you would change for more/less power. A rotor is a rotor?
Bottom Line: Yes you can switch rotors but you won't see much improvement.