If your ultimate goal is to have a traditional tack-sharp print, it's best to put the manipulations above the negative. Print quality is highest (and I realize that "highest" is completely subjective) is there's as little as possible between the emulsions. Vaseline above the negative will give you a sharper print (in the areas you want sharp) than Vaseline on glass held above the printing paper (i.e. between the emulsion of the negative and the emulsion of the paper.) In all reality, the difference may not make a difference, but heads-up anyway.