Is there a way to tell if a value in a cell has been
treated with the =TEXT formula, and then pasted back
as values?
Certainly not literally. You cannot know what was in the cell before
it was changed.
However, you can write a macro that determines if a cell contains a
formula or not.
Function cellHasFormula(r As Range) As Boolean
cellHasFormula = r.hasFormula
End Function
AFAIK, there is no way to accomplish the same thing using just Excel
functions.