In the state of Texas does a landlord have to change the locks before a new tenant moves in?

I do not find this to be State law.

I do not find this to be State law.

And I would be very surprised if it were.

The reason is this: many things are best left to the parties to work out, rather than making a law which would force them to do something that perhaps neither of them wants. If you want the locks changed, ask for it, and be prepared to pay.

Although some landlords rotate keysets, they don't have to. (Neither does a homeowner when he sells his house.) You can change the cylinder pretty cheaply, but do so only with permission and give the LL a key.