Fallout 3 or New Vegas-ish within Fallout 4? The game is vastly different from those games though, so I don't think its possible to do that even with mods in mind. I guess for the environment Dustbowl is a good try for a NV-ish world, plus use the Bullpup Bozar, Caravan Shotgun, Varmint Rifle, and NCR Ranger Armor, and NCR Trooper armor mods in the nexus and I think that's the closest to NV as it can get. Oh and get the M1-Garand mod.
For a fallout 3-ish world, I guess its easier to do that since Fallout 3 and 4 isn't that different from each other in terms of clutter in the environment. I do recommend you get Scorched Earth for the dead wasteland feel that's similar to the Capital Wasteland. You can also get the R91 Assault Rifle, Wasteland Melody's Chinese Assault Rifle with Wardaddy's animation for it. There is also a Chinese Pistol again with Wardaddy's anims for it. However, if you're willing to take it up a notch, go get the DKS-501 Sniper Rifle in the nexus to complete the set. For the armors, you don't have to get too much mods for that since the vanilla fo4 armors somehow fits FO3's art direction anyways (you know, rugged-y, dirty, torn-up piece of shit clothing with bulky armors). Lastly, you CAN try to use Calamity Weathers in the nexus. It makes the game...uhhh..gritty and dark, which I think can compliment Scorched Earth and Vivid Textures AIO pretty well. Oh get Adventurer Outfit with the Altyn Helmet, and Holstered Weapons by azar. Its basically a PUBG-esque set, but hey it fits well in the world.
Really, considering the massive turn with FO4's art direction, modding the game to be near FO3 and NV is challenging af. I changed everything from environment, to armors, to weapons, and even to the BGM and SFX in-game jesus christ. I gave up on it since, to me, its a waste of time trying to mod the game into something that it is not. That's just me of course.