This question already has an answer here:
Is it generally, to a reasonable developer, considered morally acceptable, to take a branch of an open-source repository, and start making changes to it and calling your own? You would be taking this to another open-source.
Assume that you will link to the original. Note that this is a question of what is considered acceptable, not what is legal.
If this is okay, where is the line of how much you change that allows you to call it your own?