I'm working on a Pega project that I need to change the cosmos design system to match my client's style guide and use that to do Visual designs. Basically, I don't want the Cosmos Blue color theme and need to change the entire design system theme to something else. (Button colors, Font, left panel navigation, etc.

I'm going to make a copy of the latest sketch library (Subscribe to latest Sketch library updates) and update the component styles to match my branding and use that for visual design.

What I understood is that pega updates the latest sketch library hosted in the design.pega.com once a month and if I download the latest online sketch library update, I will lose the changes I did to the copy of the live sketch in the next month's updates right? 

What is the best solution to keep a library locally and get the updates without losing the updates I did to my local cosmos library?