The roster gets finalized in planning before it gets finalized in programming, something as minor as Snake's C4 aesthetic could really be changed at many points during development, but something like making Toad playable would be decided relatively towards the beginning, and then characters would get programmed around that. So, Toad would likely be decided in pre-production, before development of the characters even starts, which makes replacing him in Peach's B move at this point fairly unlikely.
That doesn't necessarily mean he isn't playable, but at this point in development Sakurai has decided on whatever role Toad has, and isn't going to change it now. If he knew he wanted Toad to be playable, and he used the standard Toad colouring for the playable Toad, it's unlikely (though not impossible) he'd go with that same colouring for the one Peach uses.