How to remove and reinstall the theme

Hi there,

After 2 years of customization on the theme, I want to take off everything I don’t need anymore. For this, I plan to do like that :

1- I create a subdomain with lopsum pages and posts
2- I download Newsmag and Newsmag child from my Enavato account, and upload it on the subdomain
3- I customize the design in the child CSS

Once the theme is customed, I do this :

1- I go to my main site, and save Newsmag and Newsmag child on my computer.
2- On my main site, I erase Newsmag and Newsmag child.
3- I upload Newsmag and Newsmag child from the subdomain to my main site.

Now my question : is all the above the correct way to erase all the previous theme customization, or is there another way ? Any tip ? Thanks in advanced :).

Thanks Catalin :).