> For a (symmetric) rank-2 tensor field like charges attract.
For a spin-2 field all charges attract. There is no such thing as "unlike charges".
> The weak equivalence principle only requires m_i = m_g up to the sign of the latter.
I don't know where you're getting that from. The WEP requires that the trajectory of a body moving solely under gravity depends solely on its initial position and velocity. That means m_i = m_g. It does not allow flipping the sign; that would mean there would be two possible trajectories for a given initial position and velocity, not one.
For a spin-2 field all charges attract. There is no such thing as "unlike charges".
> The weak equivalence principle only requires m_i = m_g up to the sign of the latter.
I don't know where you're getting that from. The WEP requires that the trajectory of a body moving solely under gravity depends solely on its initial position and velocity. That means m_i = m_g. It does not allow flipping the sign; that would mean there would be two possible trajectories for a given initial position and velocity, not one.