Sorry about that. I got stuck up on your paragraph:

"I would want my appendices to be on the same level as my Heading 1 in the bookmarks. But i can't use Heading 1 for my appendices. Because my text chapters are numbers (1,2,3...) and my appendices chapters are letters (A,B,C...)."

Then I could not see the trees for the forrest...but, I digress.