Does the Federal CAN-SPAM Act requirement of "disclose clearly and conspicuously that your message is an advertisement" preempt the Texas Business and Commerce Code Sec. 321.052 requirement of "ADV: appears first in the subject line"?
The first question to ask is are you sending emails to individuals you already have an “established business relationship” with? If the answer is yes, the Texas law does not apply. Additionally, if you have recipients affirmative consent neither law Federal or state law applies.
Texas Business & Commerce Code 321.001
321.001 (8) "Unsolicited commercial electronic mail message" means a commercial electronic mail message transmitted without the consent of the recipient by a person with whom the recipient does not have an established business relationship. The term does not include electronic mail transmitted by an organization using electronic mail to communicate exclusively with members, employees, or contractors of the organization. Source
The Federal “CAN-SPAM” Act of 2003 has a similar exemption if the message being sent meets the standard of being a “transactional or relationship” message. Also exempted from the Federal law are messages where the recipient has given their affirmative consent. If your email message meets either of those two exemptions they are also exempt from the “labeling” requirements. Source
So there may be situations where you have to reconcile the two laws – but nothing prevents you following both.