But can you give me a couple of examples of changes in the theology?
If you read French or Arabic, there's a number of articles about the theological trajectory of the Melkite Catholics and how they-- more influenced by Gallicanism, in fact, than Orthodoxy-- started to see themselves as theologically quasi-independent of Rome (the career and eventual condemnation of Germanus Adam, who was fiercely opposed to papal authority but also, in line with most Melkite clergy of his time, believed that the Orthodox could not be saved, is a good example of this). But, for the first century and a half or more of the history of their church, they did not have a theological identity separate from Rome. If you look at the education of their clergy in the 18th and 19th centuries at the Monastery of Shuwayr, for example, there was a huge effort to translate from Latin, French, and Italian all the main works of Counter Reformation theology that was far more developed than any interest in patristics or Orthodox texts... For a much more detailed discussion of that point, I'd reccommend this article: https://www.jstor.org/stable/27667681?seq=1#page_scan_tab_contents
For what I think is a very even-handed discussion of the cultural and theological factors that led to some Orthodox in the Levant joining with Rome, I'd take a look at Constantin Panchenko's book, recently translated into English as Arab Orthodox Christians under the Ottomans: 1516-1831
, especially pp. 454-490.