What you're mentioning is theoretically possible, though if you specifically want to use curly braces you'd need to either retrieve the contents of the text file directly so the token parser doesn't remove them, or escape them.
You'd then need to implement a parser that can check each line for that sequence of characters, execute the specified command, and then make sure no output is passed along to the rest of the command for reading aloud.
If the intent is specifically to execute another command when the end of the text file is reached, a more feasible option could be to modify the command, which presumably already has special handling for reaching the end of the file, to execute a command whenever the end of the file has been reached.
What are the full contents of the command? Right-click the action list, choose "Copy All as Text" from the context menu, then paste here into a code block (click the # button)