Question about Black Templar Marshal

[SrgVigil]

Is their any rule agaisnt not being able to use and model to represent a character as a marshal? Seeing how the only Marshal character is High Marshal Helbrecht and I do not like how he looks would I be able to use a model let's say from the Chaos Marine line as use him to represent my marshal? Or is there a rule saying that you can not do that.

[Brother Wolf]

The Marshal is just a BT commander, so any suitably commander looking model will be fine.

[Trignama]

i agree with armand.... i say use whoever you like it is YOUR army