(a) Except as provided by Subsection (b), Chapter 6 and any other applicable provision of this code apply to:
(1) a meeting of the governing authority or a committee of the governing authority held on or after the mandatory application date;
(2) an action undertaken by the governing authority or a committee of the governing authority under a written consent that takes effect on or after the mandatory application date;
(3) a vote cast at a meeting described by Subdivision (1); and
(4) consent given for an action described by Subdivision (2).
(b) Prior law applies to a meeting of the governing authority or a committee of the governing authority and to any vote cast at a meeting described by this section if the meeting was initially called for a date before the mandatory application date and notice of the meeting was given to governing persons entitled to vote at the meeting.