And then later the applications arrive from the kids they got to know (and others) and the collective deans (aka junior AOs, and the boss) read and discuss them, and decide their fate.
You would need years of training and experience. You could maybe start by applying and getting accepted as a student intern in Admissions at your college once accepted.
At Yale, where my daughter went, a couple just-grads would typically join the admissions office each year as a sort of “gap year” kind of thing. I don’t know what their exact role was though. I’ve seen that at my alma mater (Swat) as well.
I commend your effort to change the admissions process but it’s not going to happen from the inside of colleges outward, it will have to be from the outside in. AOs will want to keep reducing acceptance rates, send out tons of fliers to people who have no chance of getting in and help their schools move up in the ranking.
Anyway as others have said, do a work study at the AO if you can, or be a tour guide, and then join the staff if you can after you graduate or maybe a year or two after. AOs want a couple of people who are recent grads to keep current, most of them are old like me :-). If you get on an AO and you want to change something smaller, perhaps convince them to eliminate ED or SCEA and just go with EA, which would benefit students. Right now ED only benefits the college, so eliminating that would start helping the students, who right now are stressed out, for really no reason.