First, let me share my opinion even if I did not experience to manage a signature campaign or as a manager.
As I noticed, it will depend upon on situation. If the spot is for lower rank and the application of participants was not qualified and there is high rank ready to take a lower rank and have a quality post, then, why not.
The queries of OP is will depend on a case to case basis.
16. I solely reserve the right to remove participants, disqualify posts and changing rules or pay rates.
Just like the rules that implement by Coolcryptovator, you have the right since you are a campaign manager and that is a part of your job to check quality posters and who is the right to choose as long as the applicants willing to take lower rank by their willingness.