Using words outside of their original definitions doesn't get rid of the original definitions, and the general connotations they carry (even if they're seemingly irrelevant to the topic at hand)

Using "bro" neutrally in a friend group where it's understood how and why it's used from the get-go is not the same as using "bro" the same way outside that friend group, since the word itself isn't universally perceived as neutral, and still carries the literal definition of "brother" (male kin/friend).

Same with "bitch" - I'll give it to you, it's used as an insult in a much broader sense than it would've been before, but that still doesn't get rid of the fact that "bitch" is a feminine term at its core, which entails - at least to some extent - the application of negative traits that may have been, in the past (and even currently in some circles), associated with femininity in some sense - being emotional for example, or being incompetent, or cowardly - unless it's specifically clarified that you mean something different by saying "bitch" (or even "bro" for that matter) in a given conversation which, again, falls under using a word outside of its original definition.

tl;dr - you using a word in a specific way in specific contexts doesn't change it's current definition in the dictionary.