I did make a career mode version for the Solar System 4.1 and It Should Work Easily,
Tutorial:
Download The Custom Career Mod File Here: https://drive.google.com/drive/folders/1d1OAWqoTEV0LODFIsJeFjeNxuaR5BJLI?usp=sharing
You'll Need This To Help It (Note: this mod will not work with realistic mode easily, it only works with solar system 2.1 and spacerace career file) Link Here: https://github.com/Oxeter/SpaceRace
Download The Recommended System: https://www.simplerockets.com/PlanetarySystems/View/KAQA25/Solar-System-Windows-Version
Press The Download All/Download Button, Go To Files, Then Unzip The Realistic Mode File.
Send The "Realistic Mode" Career File Into: "C:\Users\Your PC Name\AppData\LocalLow\Jundroo\Simplerockets2\Career"
Then Place The SpaceRace Mod Into: C:\Users\Your PC Name\AppData\LocalLow\Jundroo\Simplerockets2\Mods
You Can Start The Game, Enable The Spacerace Mod, Then Select The Planetary System "Solar System 4.1" Switch The Gamemode To Career (It Won't Change The Planetary System Selection If SpaceRace Is Enabled) And Then Set The Career Mode Difficulty To "Realistic Mode" And Create It.
After That, Disable The SpaceRace Mod And Restart The Game, And Enjoy It! :)
Note:
This Is A Very Very Very Early Build And It Will Be Finished Around 2026 And 2027, And You May Find Some Few Bugs Around This Mod.
Known Bugs
Doesn't Save If SpaceRace Mod Is Enabled
40% Chances Of Structures Dissapearing
The Planetary Systems Go Emtpy If Leaving The Moon.
If You Encounter the "Mods Required" Title, You Can Ingore It And Continue To Prevent Any Upcoming Bugs.
Anyways, Thanks For Reading The Tutorial.