I have a modded minecraft world, with the Hatpack modpack, a private modpack available on the FTB launcher. I wanted to change the default settings for the Farlanders mod. I updated the config settings to reduce the spawn rate of Wanderers. I changed them in notepad, saved the file, exited, and opened up my world in the Hatpack and low and behold, no changes. I tried this with other settings, like whether or not you could have the ability to fly with flying mobs from the Morph Mod. These changes also had no effect to my world. I also set them to allow me to build tesseracts in my world, which by default had the final recipe disabled. I have however had success with a newly created world, which had all the correct changes I made present in THAT world. I want it on my old world though, I had made so much progress before I found out about all these changes I wanted to make that I'd hate to have to start all the way over again.
TL;DR: Does changing config settings to a modded world apply to that world, or can you only use the new settings on a Newly created world?