Section 7.E.2.a includes this line: A pilot may adjust his vacation period by sliding it up to a maximum of 5 days in either direction.

That seems to cover part of your question. I think the other part is taken care of by the language that says: A pilot may enter a vacation slide submission during the Conflict Input Window immediately before the bid period in which a trip(s) affected by the slide (or the vacation period itself, if no trip is affected)... That "the" apparently means only one slide per vacation since you can only adjust the slide in the bid period prior to when the vacation happens.