i would say do a test swatch with whatever yarn you want to use and then see what the gauge looks like with that extra yarn. it may change it a little bit but i have a feeling it wouldn't be tooo much and if you use it with a felted hat it would shrink everything down but the fuzz anyway (unless that fuzz is a natural material of course!)
i am very partial to this
pattern. and i think it would look very cute with the fuzzy yarn! When i made it i gave it to my friend's 2 year old. I used bulky yarn and i tend to knit a bit loose i think. it shrunk down to fit her 20 inch head without any pulling over the head. (not sure if that makes sense but it basically plopped down on her head but wasn't so loose that it fell off) and since it is felted i would think that it would be pretty forgiving for them too!
yeah the curliq's were pretty horrible but i loved the look so much that i am embarking on another!