24b stock rooted easiest downgrade process?

I am currently running the 24b stock rooted and would like to get TWRP installed. I understand I need to downgrade, however what is the easiest way to do so? Do I need to go all the way back to 10c stock? Then root, install recovery and update radio etc? Or can I simply downgrade to 23c?

My goal is to run the newest Skydragon and 35b bootstack by xdabbeb to have HD calling.

Thanks!

Easiest way to upgrade to marshmallow when already rooted?

Easiest way to update to marshmallow when i'm already rooted? Will it delete all my ****? Do I need to make a backup? Thx in advance.