In actuality (and I didn't allude to it), when you unroll a compacted roll of unfaced wool insulation, it will 'fluff' up by itself. When insulation is maed, prior to packaging it for shipment to a retail store, the material is steamed and compressed.. (see how it's made, insulation) on You-Tube) so once it's unrolled. cut to size for fitting in the space, it's already fluffed and no matter how you 'stuff' it in, you'll never compress it again. Besides, putting it in there with a stick (I use a wood yardstick), you are pushing it in from the side so it will assume the space as you insert it.
As an aside, you may get some compaction, depending on how zealous you are, but you won't fully compact it back to it's shipping state.
Wear disposable gloves and a particle mask and long sleeved shirt. It's itchy stuff.