Hi There,
Thanks for writing in! If the “changes” you mean are the Customizer Settings then it should be transferred safely, but if you need to play safe, you can also backup your customizer settings on Addons > Customizer Manager > Export. You might also need to re-set your primary menu and widget areas after you switch to child theme. All your pages content and settings should be safe.
If the “changes” that you mean is a custom templates and/or custom functions then you need to copy this modified templates/functions to the child theme first before you switch theme.
Please read this post for more info on how the child theme works.
Hope it helps, Cheers!