You're misusing one thing (D mangling) for a different purpose and loose the important information about the origin of that mangling on the way to the backend. Also adding comments to explain this fact is pretty ugly.
Let's try to add a new mangle constant instead, e.g. mTYman_custom or so. If it is too much work to handle that in the backend, mTYman_custom could simply be an alias to mTYman_d.