You can cancel them if they set it in the future and you see it before it starts. I do this sometimes for opponents that are in the same Cup or CL as I am. They want to practice against my team because they know they will have to get by me at some point. I do my best not to allow that.
there is no reason to do this.
Friendly games have a different calculation and process. I have won friends who challenged me, 5-10 levels above sometimes

When a final is approaching I will actually put up a totally different formation and tactics just in case they try that.
If you 're not gonna watch your game, that's good. If you 'll play, there is no reason because you can change your formation.