Consider an atom (carbon) with a ground state valence electron configuration of:
$$ \underset{3s}{[\uparrow \downarrow]} \underset{3p}{[\uparrow \vert \uparrow \vert \; \; ]} $$
In some molecules such as carbon tetrafluoride, carbon can "expand" to a more energetic electron configuration similar to:
$$ \underset{3s}{[\uparrow]} \underset{3p}{[\uparrow \vert \uparrow \vert \uparrow ]} $$
Although these orbitals would usually be mixed together and also paired together with the opposite atoms they are attached to.
Are there any cases where the reverse can happen?
For example could phosphorous "contract" from
$$ \underset{3s}{[\uparrow \downarrow]} \underset{3p}{[\uparrow \vert \uparrow \vert \uparrow ] }$$
to
$$ \underset{3s}{[\uparrow \downarrow]} \underset{3p}{[\uparrow \downarrow \vert \uparrow \vert \; \; ] }$$
Looking at the geometry of p orbitals and taking into account molecular orbital theory I think this is always of non benefit unless possibly the materials are put under external strains such as high pressure or heat.
Also, in the cases of atoms like chromium which are "expanded" by default I'd imagine contraction to the typical state could happen.