Once I realize my aspirations of becoming a shapeshifter and/or getting a new body, what should I do also to build up a new online identity, and get away from everything that reeks of my past self?
Smiley, you're on an anonymous imageboard. You don't need an online identity in the first place.
Change any mention of your real name on any site you can find, and delete any accounts. Eventually your results will start disappearing from google. You can go to any site, make a new username, and have a new start, but I wouldn't do it on sites you've already been on because that's untrustworthy.
People keep identifying my posts when I post as anon 90% of the time.
...and I don't have any accounts or anything.