I modified the Player component from the App Inventor sources - Player. I compiled the extension and when I import it to the builder then the extension dosent appear in the section:
The extension name is 'Playerx' and not 'Player'.
I am not sure if its only happening to me. But when I search it in the Pallete it appears:
Oh thanks now it works. I dont know how I missed it to change! First time when I import the extension with category with extension dosent worked. I had to reload it twice. Anyway thanks.
My silly mistake.