The phrase "made mutable" or similar (as in, "When group policy changed, a ton of files became mutable.") might serve better than "unfrozen", for your second example.
Files being made mutable indicates that they have changed from being read-only to being read/write, while files being "unfrozen" is ambiguous because it could mean that the files changed from unavailable for reading to available for reading, vs. from read-only to read/write vs. from not-deletable to deletable, etc.
An advantage of "mutable" vs. "changeable" and "alterable" is that "mutable" is already in common use in Computer Science with the defined meaning that an object, attribute, or value is subject to change instead of being fixed: "[An] immutable object is an object whose state cannot be modified after it is created. This is in contrast to a mutable object, which can be modified after it is created."
Another possibility (although subject to some of the same ambiguities as unfrozen) is "unlocked". E.g.: "When group policy changed, a ton of files were unlocked."