If you really want to go that way, you could use something like this in your "Format value" action:
$if($eql('TTA',$upper(%_extension%)),$repl(%TITLE%,' tta ',' '),)
Please don't use this abbreviated syntax!
As found in this bug report, the abbrevation of $repl instead of using $replace can result in unwanted changes. Always use $replace as stated in the help.
This would replace the text space tta space with a single space whenever the extension of the current file is TTA. You have to adjust it to your needs and use cases.
As @ohrenkino told you: This will also remove the bold marked text from titles:
Let tta and Cathode
or
Too young tta way