While doing a little research on the reactions and statements from Texas Board of Education members who voted yes on the changes, I found little discussion specifically referring to the change from Atlantic Slave Trade to Atlantic Triangular Trade. There were other quotes and actions, however, that perhaps gives us a window into their thinking.
Another change that was made was to add the contributions of Confederate politicians to American society to the lists of people students should analyze. Texas is, after all, a southern state, and was also a slave state before and during the Civil War. On could argue they were changing the wording regarding slavery to make it more accurate, but I would have to disagree. The slave trade outlived the Triangular Trade for a long time. I see it more as an attempt by southern social conservatives to whitewash the history and paint the South in a more favorable historical light. This is just my opinion, of course.
I would caution against drawing a broad stroke of the classification pen with the idea of "White Conservatives." Conservativism is an idea that is not limited to ethnicity or race and the notion of race is not automatically linked with political leanings. I think that the renaming of Atlantic Slave Trade to Triangle Trade might be appealing because it emphasizes the commercial nature of exploration in the New World and the advancement of commerce. The "Slave Trade" carries with it negative implications that might prevent one from understanding the economics of the time period and the growth of mercantilism as an economic policy that preceded capitalist enterprise. That being said, I, for one, do believe that the renaming does obscure the fact that much of the development of the New World came at the direct cost of others. Namely, slaves. Yet, those that wish to rename it might see it differently and to remove the slave element would be done to advocate a more desired objectivity without the negative reality attached to the term "slave trade."