use two cars one with the boat on drop it in to the water. drive the boat away from the ramp, when he returns with the other car with the new trailer put it on adjust all roller too high. than park out of the way somewhere and you can than slowly loosen the rollers and they will come down and the boat will sit in place final adjustments can be made latter.
this way will affect others the least.
But if it was me I would also try and do it on a windy day... shouldnt be too hard to find one of those