"Down" means lying on the granite, not removed entirely.
The support poles and cross boards get removed so that they don't get ripped off by the winter snow/ice.
Not terribly difficult if the rock is dry. Quite dangerous if it is icy and/or wet.
Much less margin for error than the summer conditions.
With this years currently near record snowpack, there will likely still be substantial snow in April.
(i.e. this would require skis/snowshoes, winter navigation skills, etc)
i.e. this won't be a "hike" in April.
In April, You might want to do just the Nevada Falls loop, Yosemite Falls, or even Hite Cove (if the Merced River Valley poppies are blooming)