Changing Themes

I’m currently working on SKT Black theme and it not yet a live site. I need to know if I change the theme to another one – e.g.to Blackoot Lite, can I change back to SKT Black and still have all the customized updates and addins as it currently is? Will the new theme incorporate all the edits and changes I made to css pages?

Simply put, do I need to “preserve” the current SKT black site before I activate another theme? And how would I be able to switch back and not lose the work and customized edits I’ve done?