I accidently made this super long, but I'm posting it anyways.
Black Tejanos:
In a world in which Mexico* never lost the Northern territories, and where some other stuff happened and happens, some Black Americans in the 1880s would go West to Texas* for a new life. And while they do find more acceptance in Mexico* , then they did in the US at least, Black Americans at first kept to themselves on the way of religion and tended to stick for the most part to border towns/cities. Since most never leave Texas, for the first few generations at least, the descendants of the Black Americans who went to Mexico* would be called Black Tejanos, even if they weren't born in Texas, but in another part of Mexico*.
At first, they only spoke English and only learned enough Spanish to get by, but not enough to fully join in the greater Mexican* national community. Later on, the children would go to school and learn Spanish, but they would still speak English at home. In the end though, Black Tejanos would fully adopt Spanish as a native language, though their particular variant still has quite a bit of influence from Black Southern US English in particular, even though it really isn't English.
In Texas while the mass majority was Iberian Catholic, Protestants formed a burgeoning majority on the very Eastern areas of the state, and most of that is due to Black Tejanos. Mexicans* didn't mind much as the nation was and is pretty tolerant of non-Catholics in general. Though the Black Tejanos were seen as a curiosity in particular due to the liveliness of their churches. A liveliness that would later spread to Mexican* churches in general as future priests and priestess would listen and hear the songs and celebration of the Black churches, and would later adopt that into their own churches. Indeed, the musical styles of the Black Tejanos would not only spread to the Mexican* churches, but would seep into Mexican* musical culture as a whole. More (Black) American influences would come in as well, as the Black Tejanos would stay in contact with their brothers/sisters back East in the US, and would take aspects of the music there into their own array of influences and then that would go on to pile into Mexican* music as a whole.
Economically, Black Tejanos did increasingly well as the years rolled by. Unlike in the US, Mexican schools were and are all equally funded to be pretty high standard, so Black Tejano schools aren't lacking in good teachers, materials, etc, despite the poverty of the people who lived there. University was also in easy access for the poor, giving Blacks lots of opportunity to move up in society. Indeed, many would go on to become comfortably middle class.
But, they would not forget home, as in the 1930s various Black Tejanos would go to the US to try to bring their new found wealth to their American brothers and sisters. This would work to varying degrees. Some would go on to become the centers of their community, while others would return to Mexico in defeat as they quickly realized they aren't American and that their counterparts their didn't appreciate the "Black savior complex" that the Tejanos carried with them.
By the modern era, Black Tejanos have gone onto become highly integrated into Mexican* culture/society. They no longer live as separately as they did before. The old Black Tejano communities in East Texas are less Black American and have lots of new blood from the rest of Mexico*. While you still see most people in those areas having African features, these features are often subtly combine with ligher hair/eyes/skin and facial features that are more commonly seen in Asians/Indigenous/Europeans, though most Americans would still describe these people as Black. There's also more non-Black people in general within those areas as well, though the areas themselves are still famous for their history as a refuge for Black Americans, and its something that those town/cities still celebrate. But still, few people in the old Black Tejano communities can really say that they are purely of American descent and many now have Hispanic surnames and given names. The connection between them and their cousins East of the Mississippi has also been weakening as outside of the edge of American border states, most Black US people would just see another Mexican* when they see a Black Tejano, even if that Mexican has Black features. This also goes across the border as well, as the newer generations of Black Tejanos have less and less of a connection to the US, especially since lots of young people would find themselves leaving Texas for the Californias and other areas of Mexico . Nowadays, Black Tejanos, which is a term that is becoming less common in regular speech, outside of historical contexts, are just regular Mexicans*.
Nonetheless, this ethnicity, though not as distinctive as it once was before, has gone on to leave a mark in Mexican* culture and history. Many Mexican* celebrities, be they actors/artists/writers/ singers/ politicians, etc have origins that go back to the original group of Black Americans who arrived in East Texas all those years ago. And Mexican* culture as whole has adopted various traits that were initially restricted to Black Tejanos. Showing that although they no longer stand out as they did before, the legacy of the Black Tejanos still remains forever ingrained into Mexico*.