I'd take the votton wool off.
By the time the cotton wool disintegrates the moss will have attached.
No need for cotton wool, and it will break up in the tank.
I would think that the cotton wool also contains contaminants to clean it like bleach etc. also
Just trust to nature. Does someone come along and put cotton wool on bogwood for the plants to attach to? Noo
They also dont use cotton wool but we have no river banks coming up from our tanks for the moss to gradually creep into the water, and we are after a much speedier effect than years of gradual growth.
Andy