atom-text-crosser package

Allows you to search for a regular expression in a selection (by default all alphanumeric characters and some symbols) with a string (by default X) Use Ctrl+alt+x to crossify stuff (no Mac keybinding as of yet)

NOTICE

This doesn't save your text when it replaces it, and the only way to revert it is to undo it. Once you've replaced a block of text, that's it (unless you undo of course).