Well I don't think Siobhan would use it, if she were Head Girl, but I do think Moebius would use it if he were Head Boy. But there's no way Moebius will be Head Boy, his marks aren't good enough.
Moebius was also really cross that Moran put it on a Slytherin. So if he did get to be Head Boy, I think he'd mostly use it on other houses. Which would be good for me but bad for you. If Percy DID use it he'd probably go out of his way to start with a Gryffindor so no one would think he was showing favoritism.
Re: I Solemnly Swear That I Am Up To No Good
Moebius was also really cross that Moran put it on a Slytherin. So if he did get to be Head Boy, I think he'd mostly use it on other houses. Which would be good for me but bad for you. If Percy DID use it he'd probably go out of his way to start with a Gryffindor so no one would think he was showing favoritism.