Brushed Dc Motor to Reluctance Motor
The rotor of a DC motor will not work very well as the rotor for a reluctance motor. The rotor of a reluctance motor should have alternating low reluctance (iron) and high reluctance (air) paths from the surface of the rotor through its interior. The low reluctance areas of the rotor of a DC motor are the narrow slots containing the windings. They are designed to be no larger than necessary to hold the windings. They are very narrow at the surface of the rotor and said enough to contain the coils in the interior. See below.



It would be a pointless to design and construct a stator for a reluctance motor without using a suitable designed rotor.

Mechanically Commutated Reluctance Motor

You may be asking if a reluctance motor can be mechanically commutated. There seem to be some patents for mechanically commutated reluctance motors. There seems to be no reason that should not work. However, the stator and rotor would need to be designed as reluctance motor components, not adapted from a DC motor. The commutator would need to be quite different from a DC motor commutator.