It was actually a very technical question and Ok, then I’ll try to answer the question myself.
Theme Switcha shows a user a completely different theme, as if it were activated. Only some functions are to be taken with caution (See Important Notice from Theme Switcha). If you change the blogname for example, it will be changed globally for all themes because there is only one options field (blogdescription) in the database for it.
But since the pro-theme options are stored as separate database entries starting with “x_” I don’t see any problem to make changes. And also the headers, footers and content created in the builders are stored in the posts table as post type starting with "cs". So also no collision with other themes so far.
For all interested people here is an article from the developer site of wordpress about saved theme options: https://developer.wordpress.org/themes/customize-api/customizer-objects/
So from my point of view it is no problem to set up a user temporary theme via Theme Switcha, as long as you only use functions that are purely used by pro-theme. I’ve tested it on a test-server and Theme Switcha is a great plugin to prepare a theme for release in the background, with caution on the exceptions described above! (And by the way, if option is enabled, them switcha could also be used in front-end so user themeself could switch a theme)
Please correct me if I have missed something important here.
@Regnalf