Hello,
I have read the reques carefully. The only way to change the wroding is to rewrite it in PO file and free Loco translate is used not only for transalation but for changing the strings as per your needs. Please check the video tutorial to see how to save the translation file properly, as soon as you change all the wording you can even delete the plugin and all the changes would remain.
If you try to change the wording just in code it would reset with each update and you will have to do the same each time after update.
If you have any questions please feel free to contact us.
Best Regards