Originally posted by xplosive58
If im play in a mode, say Lydian, with a C progression playing in the background...

What do you mean by a C progression , Cmaj progression ?

If the prog is C maj , you can play F lydian by altering the progression to end with an F .

If you want to play a C lydian mode , then the C progression should be a C lydian one ... i.e. Gmaj progression , but with the C as the tonal center.