the important part missing in my example is the 'vice versa'. the canonical example is:

> sledge() { tr ab ba < $1 | sponge $1 }

then, you might undo a change you already -p added.

more convincing might be (using gnu sed):

> sledge() { sed -i s/identifier/long_identifier/ $1 }

a second iteration will eventually generate long_long_identifier.