Hi everyone
Thanks for this thread - I couldn't find the Status badge tweaks either. The key, I think, is having the product gallery open in your design editor, not just a single product page. If the product gallery page is open, the list of status badges design tweaks appears in your design menu. For me it was right at the bottom.
I think that's what solved it..!
Hope this helps someone, it was an 'a ha!' moment for me after much searching and getting frustrated!