My boyfriend is in postgrad halls and he hadn't got a lot of necessary stuff so I've ordered packages. He went to ask if there was a way for me to collect them rather than him and the staff let him know there is a 3 night rule on guests. I've planned to stay for a week (and will not come again for months). I think as long as I don't order anymore parcels they won't notice.
However, if they do, is this legally enforceable? I wouldn't want him to get kicked out. It's been a long time since I was in halls but people had guests for however long they wanted and as long as they behaved well, not an issue (one of my flatmates had someone over from Canada for three weeks and no-one batted any eye).