Wiping the areas with an anti fungal cream wouldn't hurt...and may help.
It would have no harmful effects.
I've been touting the "dollar store" athletes foot cream. Same active ingredient...
Honestly, the whole shell looks very dry and flaky. The terrarium really needs to be fully enclosed. Are the temps and humidity high enough? Swapping out your substrate won't do anything. The carapace isn't in contact with the substrate anyways. Keep the humidity high, clean the areas with some betadine and a tooth brush and apply a little bit of clotrimazole cream. No big deal. I've actually experimented using Extra-virgin cold-pressed coconut oil (there is a thread about this on here somewhere which inspired me to try it) with stuff like this. Might be worth a shot.