The Constitutional Convention of 1866 was called to make the state's Confederate Constitution conform once again to the Constitution and laws of the United States. Additionally, the convention made substantial - but limited - changes to the institutions of government. The work of the convention amounted to a series of amendments that together with the existing Constitution of 1861 became known as the Constitution of 1866.
Most notably it increased the Governor's term to four years, changed the method of selection of the Comptroller and Treasurer to popular election, and specified in detail the jurisdictions of the various courts in the state.
The beginning of the trend toward constitutional establishment of specific public policies - as opposed to broad descriptions of public authority - can be seen in the work of this Convention. The new Constitution contained "elaborate plans" for a system of public improvements and for a state public education system directed by a superintendent of public instruction.
Like the Convention of 1861, this convention aimed for relatively modest changes to the existing document, which traced its origins to the constitution of 1845. Nevertheless, a significant disagreement unfolded regarding the legitimacy of the laws adopted during the five year period under the Confederate constitution.
On the one hand, Radical Republicans led by Morgan C. Hamilton argued that all laws adopted since secession in 1861 were null and void, because secession was null and void ab initio (from the start). This interpretation came to be known as the ab initio view.
Moderates led by Andrew J. Hamilton argued that secession was nullified as a result of the war. Adherents to this view preferred the more pragmatic approach of accepting all laws that did not conflict with the laws and the Constitution of the United States. This view is supported by the "basic rule of international law that holds that when sovereignty changes, general law does not change until specifically altered by the new sovereign." 
This debate posed very real concerns for economic and political stability, as contracts, agreements, and government policy made over five years would need to be redone. In the end, the ab initio view was rejected by the convention, the Republican state committee, and even the occupying military. 
6 llink: Spanish Law, The Handbook of Texas Online. [Accessed Mon Jun 30 9:24:25 US/Central 2003.]
7 link: Ab Initio Question, The Handbook of Texas Online. [Accessed Wed Jun 18 19:47:35 US/Central 2003.]