And that is not the point. I object to your 'Platonic' argument for it.
@raccoonmasks answer makes sense: yes, one can reshape the stones in a wall, reducing their size where needed, and thereby provide a way through it - by Muto magic. MoH p.50 MuTe 10 Blunting the Iron's Bite is an example for this kind of Muto. The SG might perhaps impose Intelligence + Finesse or Intelligence + Craft: Stonemason rolls to check whether the resulting wall with the opening remains standing. But all this has nothing to do with Platonic universals.
Cheers