There are plenty of country codes that when reversed become a different, valid country code: e.g. Israel (IL) when reversed is Lithuania (LI); Australia (AU) becomes Ukraine (UA).
Whether "reversing flag emojis" causes such transformations will depend on what is meant by "reversing", which is kind of the whole point here: there are a number of possible interpretations of "reverse".
Whether "reversing flag emojis" causes such transformations will depend on what is meant by "reversing", which is kind of the whole point here: there are a number of possible interpretations of "reverse".