When you modifiy the profiles.json file you MUST completely restart JOPLIN
BEFORE doing anything else.
Sometimes the text editor also create issues if you don't close it before.
(thinking it's a kind of restart), the profiles.json will be overwritten.
The profiles.json is not easy to manipulate at the beginning. You have to try many times. The good news is that it's safe for data. It only concerns the way JOPLIN understand the directories profiles.