Many other characteristics are technically mutable - you can change your place of worship, you can chemically alter your skin color somewhat, you can have surge

Many other characteristics are technically mutable - you can change your place of worship, you can chemically alter your skin color somewhat, you can have surgery to look younger or older, etc. However, we still consider them "immutable" characteristics insofar as we consider that employees should have zero right whatsoever to request that people change them unless they themselves want to.