I liberally use rekinning to make my game feel different.
Don't want plate armor, but don't want to redesign the rules so as not to nerf the defenders? Let the players use plate but story wise they don't have armor.
I also give my players a little bit tighter character creation guidlines, if I feel that it will enhance the story.
Don't want to have a high magic start of a game? Start everyone as a martial character, and let them retrain their class after a little while of using the multiclass rules for their magical training time. A 1st level martial character with the MC wizard feat and that has stats that are more fit for a wizard will definitely bring back the feel of the 1st level wizard in earlier editions. After whatever time period that you feel is appropriate to have characters wait for magical abilities, have them retrain their class. Nerfs the heck out of non-martial characters, but that is what you basically said that you want. I take many liberties with the retraining rules. This idea is one I have no problem with.
Want the characters to feel less powerful? Use higher level opponents. Reskinning monsters is really easy.
I guess that a combination of limiting equipment options would nerf the martial characters pretty well, and requiring retraining to become a non-martial character would nerf the non-martial characters. This together will probably nerf the character well enough that you won't even have to use any higher level opponents. Easy fix.
It seems like the "Off the farm" feel is really easy to get, you just have to adjust a few things. The first is what is acceptable as far as character creation goes, including allowable equipment, races, and classes. The second is how you describe characters and their relationship to the world. "Off the farm" is not an in-game construct, it is an in-character construct. Description is everything.