"Cultural appropriation" has lost some meaning through abuse. It was originally coined to cover specific circumstances. Not all use of cultural elements by someone from a different background is appropriation. The criteria are something like:
- must be a dominant colonial culture and one violently subordinated
- appropriation by the dominant culture
- the appropriation takes the thing out of context, usually making it less serious or trivial
- the same thing done by a person from the original culture wouldn't be respected
So for example the wearing of NY Yankees baseball caps doesn't count as appropriation because it fails all those tests. The adoption of Japanese cultural items by anime fans can be trivialising, but the dominance is not strong and it's not alongside anti-Japanese racism, so it fails most of the tests.
Also the ideology is that people are of equal intrinsic value and should be treated with equal respect, not that they are currently equal or should be blindly treated identically.
So, in a hypothetical future world where there is no more anti-blackness, people might stop caring about blackface. I don't think that's within our lifetimes.
Sincere attempts to adopt a culture aren't considered appropriation, such as marrying in or genuine religious conversion.