There’s no general rule for signature campaigns in the forum. In fact, you won’t even find anything about signature campaigns in the official forum rules.

Every campaign has its own manager, and their rules might differ from each other. It’s really up to the manager’s discretion. But generally, what advertisers want is to make the campaign successful. So, if you can find high-rank members who are willing to be paid at a lower rank rate, most managers would allow it.

However, there’s one campaign manager I noticed who doesn’t allow that, and that’s Hhampuz. Based on my observation, if the opening is for a Sr. Member, he will only hire a Sr. Member, even if a higher-ranked member applies and agrees to a lower rate.