Boosting a User

I think the way to do that is with a role requirement for the rank. You can create a rank where the only requirement is a role. Then you could manually assign that Rank by giving the user the required role.

Some things to keep in mind, rank is awarded by going down the list and finding the first rank the user meets the requirements for. So, the rank's position in the list matters. 

Also, remember you can have multiple ranks with the same name but different requirements. So, for example, if you have a rank named "Expert" that requires 5 accepted solutions, but you want to be able to boost a user to that rank manually you can create a second rank named Expert that requires a role instead. You could achieve the same result with a single rank with a rank formula like this (net_accepted_solutions >= 5) || hasRole("Product Expert") where || means or.