KiwiGrip say you can directly apply KiwiGrip on KiwiGrip.
Btw. For preparing slightly rough surfaces I learned something from a French guy, who is a painter by trade
I tried it on Lady Rovers aft deck
before applying KiwiGrip.
He told me to wet wash, scrub, rinse & dry the deck with this before, basically it keys the surface enough up to allow paint to adhere well. Not sure if something similar exists in jour neck of the woods though.
In our case it worked pretty well!
Took about one hour to prep instead of several hours grinding off old antislip surfaces.
This is the stuff: