Hi, suchAnight
Yes, I've been going through the national highway system and doing some downgrading and upgrading of certain ways.

As stated in the OSM Wiki (https://wiki.openstreetmap.org/wiki/ES:Mexico/Red_Nacional_de_Caminos#Clasificaci%C3%B3n_de_la_Red_Nacional_de_Caminos_[3][4])
The roads that form the "Ejes de Transporte" established by the SCT (https://wiki.openstreetmap.org/wiki/ES:Mexico/Ejes_de_Transporte) are those which will be calcsilicate as trunk or motorways.
In the link you can see a summarised map of this "Ejes de Transporte"

In this website (http://datosviales2020.routedev.mx/) which is provided by the government entity SCT you can view more in detail in "themed maps" -> "Ejes de Transporte" which are the roads that belong to this classification.

Thank you for writing and I'll be in touch if you have any more comments.