I had edited one CSL file to fit my needs. But every time I restart the pc I find these changes gone and I have to reinstall the CSL file once again. How to solve this problem
highly unlikely -- Zotero would only revert a style with the same ID. Post your style exactly as you're using it now to gist.github.com, create a public gist and link to it from here.
https://www.zotero.org/support/dev/citation_styles/style_editing_step-by-step#change_the_style_title_and_id
That's the ID. You didn't change it from the original, you just changed the title.