Hey you should keep the logs of what modifications are you making if you want to enjoy the future updates of plugin otherwise it would be always a problem for you.
So my recommendation make a log file and save in your local computer.
Mention Filename for example.
computer-repair-shop >> assets >> admin >> css >> style.css
enter the code you have added yourself. So in future you can add that. This would save you time always thanks. And you don't need to go behind every update you can always check if that update have something you want to use or not. Cause some small bug fix updates are not worth doing all again.
thanks.