It is probably not a lot different than changing stats on a RPG, with a dash of text editing. It will likely be full text editing (video for others playing along at home https://www.youtube.com/watch?v=vn2ZptkliVY
) rather than some graphics based monstrosity but OK. Looking at the video I am not sure what the stats are, and if there are any hidden values (it could be basic and just key off the value, the staff search has a rating though so who knows). According advanscene the game is only 32 megabits (4 megabytes) which is tiny for a stats driven game so maybe not so much on the crazy hidden things.
Year (4 minutes in the video for an example), and I don't know if we are handling leap years and making sure it is the proper day of the week as part of this, might take a tiny bit of looking at the logic involved to handle. I imagine it will probably be a number counting up rather than some abstract date code, but I am prepared to be surprised. Anyway similar to making a time/ammo cheat then step one is finding the time value in RAM. Once you have such a value you will be able to look into how it changes with the date on the screen and use that to ultimately change what goes.
This is an odd game to be hacking, we have certainly seen people hack sports games to reflect current players and equally spent time messing with SNES and equally old "simulators" but it is not like football management games are unrepresented among current games. To each their own though.