Each time I need to select it.
Using version 1.7, MW 1.39.
Sorry about that - generally the main namespace is indeed selected by default, but you must have some PHP configuration where the code didn't work. If you apply the change here (a one-line change), hopefully it will work for you.
Thank you so much Yaron, looks like code changed a lot since 1.7 and that line cannot be found in my version: https://github.com/wikimedia/mediawiki-extensions-ReplaceText/blob/REL1_40/src/SpecialReplaceText.php
The line has changed, but you can still make this change - it's on line 679.
Yes, but the source line is quite different, for example the one starts with xml and the other with html. This was the end result of that change: https://ibb.co/jgkMPn8
Sorry, I meant that you should just make that one string replacement within the line, not to replace the entire line.