Living in MEX I and flying AM frequently, I would suggest you get there early, and get a seat assigned, they do not have a formal bump process it tends to be chaotic since little can be done at gate they cannot issud etickets at the gate they can't issue BD at gate all manually written! They will tend to tell the last people in line they arrived too late and flight is closed, sorry ... you were to arrive 2 hours before etc and then start the re-book process. This a national flight in Mexico, if you want to get to MEX get there early ... little recourse. TIJ might be different/more advanced station since they have the NRT flight but not a chance I would want to take.