My obviously IMHO response.
Two ways to approach this.
First way:
Let us accept as our premisses that:
(a) there exists such an entity as “God”
(b) this entity has the traditional attribute of omnipotence
© to be omnipotent is to be able to bring about any condition whatsoever, where
(d) “any condition,” a collective reference, is stipulated to subsume “condition-1, condition-2, condition-3…condition-N” such that [only (NOT (any one of: conditions))] is excluded. (That last one just means that “any condition” is defined as including “every condition individually”!)
Pi is the name of a certain string of numbers that begins, as I recall, 3.1416. (Or–that’s a useful approximation.) It is defined as the ratio of the circumference of a circle to its diameter.
No one of the terms “3.1415…” or “circle” or “diameter” or even “string of numbers” is directly synonymous with any one of the rest. They are all logically independent; in the old terminology, they are related synthetically, not analytically.
It follows from the premisses, then, that God can alter the particular relationship under discussion.
I will add only this proviso, from my metaphysical stance: we are allowed to claim that God can do anything however DIFFICULT, but we can’t claim that he can do that which is so profoundly inconceivable that our attempts to refer to it are unintelligible. The notion that a VISIBLE diameter of a VISIBLE circle is shorter than its circumference is, I think, part of what we mean when we say, “Look, that’s a circle!” God can adjust the part after the decimal point, but I’m not so sure about the 3.
Second approach:
Take “flat” space, and curve it uniformly, like the surface of a sphere. The sphere can have a radius as large as you like–how about a hundred trillion light years?
Now a circle is unaffected by such a change, but the ratio of the diameter to the circumference IS affected. Thus God could alter Pi by bending the universe.
I would prefer to have Pi exactly 3, thank you.