So ... I remember being so upset about sims medivil not being a sims game with a medivil coat of paint. so i was wandering... is it possible to just mod sims 4 to being medivil setting? Like starting as a woodsmen who eventually rises to kinghood?

Big things are changing the work uniforms to medivil themed jobs like all police in the game dressed as knights. and All cars being replaced with carriages. Cell phones reskinned to like... a magic caunch shell for all i care. Computer called a crystal ball. Firefighters as guards as wel, uhh all that stuff. Is it possible?

Unfortunately because of the way the game generates random sims who then do walkbys, it's pretty impossible without your immersion being constantly broken unless you find a mod to make every single sim stay indoors and stop the game from ever generating new sims.

You would need to overhaul every single piece of furniture building and clothing and disable every single piece of EA clothing for random so sims won't spawn it on ageing up. Plus you would been to completely overhaul the food and recipes for cooking, not to mention some lots are completely un-editable. :\

It's not "just a reskin" you basically have to make an entirely new game thrown on top of the original coding.

So... if you want to do something like this sims 3 is the only option?

I see you've asked about this in the Sims 3 forum and the Sims 4 forum, but you never asked in the Sims 2 forum!

There are quite a few Sims 2 players who do something like that with their game. I'm not really into that stuff, but here are two sites that I know of that offer the kind of mods, default replacements, etc. that you might be interested in. Ask in the Sims 2 forum and you might get more suggestions.

Plumb-bob Keep
http://www.medievalsims.com/

The Medieval Smithy
http://themedievalsmithysims2.blogspot.com/

Since any texture, mesh, or animation can be overwritten, it is possible to make the game look and feel medieval, but to do it really well, the sheer size of the mod would be nearly as big as the game itself, providing you don't touch the audio files aswell.

If you want a medieval sims game, I think a heavily modded Sims 2 is the way to go. There are a good number of medieval simmers in that community, and you can find a good bit of stuff, and change almost everything if you have the desire to do so.

As well as PlumbBob Keep and the Smithy, I also highly recommend Almighty Hat's site, too: https://hat-plays-sims.dreamwidth.org/ .