It is pehaps a bit misleading to think of these separations of forces as historical events. Yes, if one extrapolates back, one can get a time when the temperature was higher than the energy scales where these separations appear. However, these separations are fundamentally governed by energy scale rather than temperature.
Today we have access to energies ranging over a vast number of scales, all the way up the just above the electro-weak scale, with the aid of the LHC. On the low side, we can cool things off to just above absolute zero temperature. So if forces would separate further, we would probably have seen it by now.
Moreover, from a theoretical perspective, we know that the electromagnetic force cannot separate further. When forces separate into diffrent forces due to some symmetry breaking, they had to come from different degrees of freedom, existing in the original force. The forces at the higher energy scales are non-abelian gauge forces. As such, they contain as many degrees of freedom as there are gauge bosons. When symmetry breaking occurs, some of these gauge bosons start to behave differently from the others. Some may become massive, as in electro-weak symmetry breaking.
In the case of the electromagnetic force, there is only one gauge boson left: the photon. So one cannot get different forces from electromagnetism any more. The only thing that can happen is that the photon can become massive (as in the case of superconductivity). Below the scale of this mass, the force would effectively disappear.