I don't have a lot of experience coding so I'm sorry if this has been answered before; I couldn't find anything that helped.
I just completed a project on a Raspberry Pi that runs some RGB LED strips via PWM. I have a program that runs the lights and works fine with a few different modes (rainbow shifting, strobe, solid color) but with each new mode I add the program get longer and more convoluted. I would like to have each separate mode be its own script that gets started or stopped by a sort of master script. That way I could easily add a new mode by simply writing a separate program and adding it to the list on the master script instead of mucking around inside a giant program with everything in it and hoping I don't break something. I guess what I want is a simple way to start a python script with some specific setting (Determined by variables passed from the master script) and be able to kill that script when the master script receives the command to change modes.
Keeping your code modulable is indeed a good practice ! If your code is not Objet oriented, the best way is to create another python file (let's call it util.py) in the same directory as your "main". You can simply include util.py with the following command at the beginning of your main code : 
        import util
And then when you want to use a function that you've defined in your util.py file, juste use :
        util.myFunction(param1, param2,...)
How to start and stop scripts using another script?