It's kind of like the law that bans the discharge of firearms in city limits. The governor shot a coyote whilst out jogging within Austin city limits, allegedly to protect his dog. He admitted he used a P3AT.
Even if we were to accept this statement as accurate for the sake of argument, it would only prove that there are variances in enforcement of the law--something that might reasonably be expected over an area as large and diverse as TX. It doesn't prove anything about the legality of Perry's actions or of the legality of OC in TX.
OC is clearly against the law everywhere in TX. Are there TX LEOs who might look the other way? It's likely. Might that attitude be more prevalent in some areas? Quite possibly. But if one were cited, one would have no way to claim justification or exemption unless the limited circumstances I listed earlier applied.
For what it's worth, TX state law doesn't cover discharge of firearms in city limits, that's an issue addressed by municipal or county ordinances. State law does provide an exemption for discharging a firearm "in a public place" when there's a reasonable concern about an attack by "dangerous wild animals", a definition which includes coyotes.
Given that TX state law provides the exemption, it would not be legal, in my opinion, for a county or municipal ordinance to criminalize such an action due to the state preemption law applying to firearms.