When I was competing in the local Biggest Losers contest (which I won twice, btw

) the only modification I'd do is not train my legs heavily - with strength training, NOT cardio like elliptical, bike or treadmill (those are cardio) the day before an official weigh in. I tend to gain around 1-2 pounds due to water retention the day after strength training my legs. Cardio never does anything to my weight short term, except maybe
temporarily lower it due to dehydration immediately after.
Now that I'm not in a contest for cash, it doesn't matter, I'll train my legs any ol' day I want to. Scale fluctuations happen for no good reason, so I don't mind when they happen for a good one. In addition, everyday is weigh in day for me!
If you're not competing for cash - assuming this is your own personal weigh in - you're not benefiting AT ALL in the long run (or short term) by skipping a workout for a weigh in. It's just manipulating the scale, not your actual body weight. Doing the workouts, regardless of what day it is manipulates your actual body weight for the better long term, as you know. You are working out for positive results, not working out means less results.