Your mod is missing the necessary language strings!
Editing the
<!--green text--> in the body of the buff doesn't change the in-game text. You need to change the text contained in the language strings if you want to override the text you see in-game.
You can add them using S4Studio's String Table Lookup Tool:
To find the strings associated with your buff, look for the key contained in the buff_description. Don't include the 0x at the beginning.
Paste that value in the search box. The relevant strings will pop up (in many different languages). Add them to your current .package.
Once you've added them, it's time to change the text. You can edit all of them if you like - but you only
need to change the text for the English string if you play the game solely in English. Click on the relevant string, then go to Edit Items.
Alter the text to say what you want, then click save. Afterward, save your .package file.
Delete your localthumbcache.package file, then try it out in game.