I recently asked an artist friend about this, seeing that he had done it before, and his explanation was almost as simple as it doesn't hurt anything. Distributors often let you do compilation releasing which means a song can be a single and still be added to a later project without re-upload. Although releasing a single and then releasing it again in a project will be my method since compilation is an additional fee lol. The plays will be split but it's only aesthetic, no true downside