Texas could always shut down power plants providing electricity out of state. That will curb their CO2, and cause brown outs all over the west and central USA.
What America needs is a three week blackout. A small reminder of the nice life we live and what it takes to keep providing it.
And as Perry says, "...action is being taken to protect the Texas economy and the jobs that go with it, as well as defend Texas' freedom to continue our successful environmental strategies free from federal overreach."
As gogogodzilla points out "What can the EPA do? They have no enforcement arm".
I'd be happy with a 2 year harassment campaign, ignoring the EPA, multiple court fights, unofficially causing power outages in their offices, and just slowing their progress using every trick in the book.