The short form needs to be a hotkey

when you want to modify selected text.

You can also use a regular short form, but in your entry you need to add the "gimme_time_to_select" snippet (which is a Stop command) before your Replace All command. So you type your short form. Nothing happens - it just allows you to select the text where you want the replacements applied, then you resume your command entry by just hitting F8, the Resume key after a Stop command.

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