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.
The statement "Muto cannot affect the properties that something has naturally" keeps coming up. I'm still fairly new to this game, but there are two different ways of reading that sentence. I'll rephrase it for emphasize the difference:
"Muto cannot affect any of the properties that a particular instance of a natural object currently has."
"Muto cannot affect the platonic / essential nature of an object, nor can it change the class of objects to which that particular object belongs."
Example: You want to change the color of a rock you're holding.
Means Muto cannot do anything at all. Color is a natural property, so it couldn't be changed by Muto.
Means Muto CAN temporarily change a property of this one particular rock, but Muto cannot change the universal template or overarching class of objects called "rock" (e.g. you cannot change the platonic ideal of a rock), nor can you change the essential nature of this particular instance of a rock, so whatever changes you made would only be temporary.
Are there other interpretations of that line which I didn't think of?
So if a stone is not naturally green, turning it green can be done with MuTe or MuIm.
Consider:
So Muto can be used to temporarily achieve a natural state of a blade - like being warped and blunted.
Both might be because of:
In this it differs from Creo, Perdo and Rego magic. But adding properties is powerful.
You have:
So no Hermetic magic can change something's essential nature, unless it is maintained. This includes Muto magic. Hermetic magic, including Muto magic, can change something's essential nature temporarily, though.
also limits Muto in a way: Muto needs to keep something to add properties to. Separating a target with Muto into several things would put a lot of stress on the concept of adding properties to it. E. g. arguing, that turning a boulder into a pile of building stones adds some property to the boulder, is very hard. So is arguing, that Muto can turn a piece of metal into a working armilllary sphere with all its moving parts aligned.
I think the point is that it isn't enhancing (Creo) nor diminishing (Perdo) nor naturally manipulating (Rego) nor learning about (Intellego), but changing (Muto). Make people a little stronger or a little smarter? Creo. Make people less alive? Perdo. The problem comes in when people try to abuse "change": I'll change people into a stronger or smarter version of themselves. I'll change a people into a dead version of themselves. I'll change people into healthy versions of themselves. I'll change where someone is located. I'll change how I see the world. Etc. If anything isn't the same, there is change. But that doesn't mean we want Muto to replace all of the techniques.
Can I replace "MuTe(Au)25 Short step of the ghost" (MoH92) with a spell based on "Level 5: Destroy one aspect of dirt, such as its weight or its cohesiveness." (HoH:S37)?
Might need a Rego requisite in order to not interfere with the integrity of the structure. As solidity is part of the essential nature of stone, the effect should have to be maintained or otherwise the the solidity will be restored. Correct?
Makes sense, and follows HoH:S p.38 Hauberk of Sublime Lightness.
This would then be Pe(Re)Te 25 (Base 5, +1 Touch, +1 Part, +1 affects stone, +1 Rego requisite adding an effect), right? Using Rego then begs for an Intelligence + Finesse roll imposed by the SG, to see whether the spell props up the wall adequately.
Covenants p.49 box Rego Craft Magic is not the only reason to apply Int + Finesse to Rego spells.
For a particularly troublesome and mandatory application of Finesse see ArM5 p.135 Seven-League Stride.