Have you RTFM on Studio Mode? You can change in the Preview window some things that have to do with composition. You run into issues (as alluded to before with Duplicate vs Referenced Sources) if you try and change a Source
For example, I use PowerPoint as a Windows Capture. There is a single Source... I can't change something in PowerPoint itself and not have that change in the Studio (Live) Window. That is NOT an issue with OBS Studio.
So, it depends on what you are changing, exactly. Some things can be changed in Preview, and wait until you transition that to Studio/Live. Others no.
So, relax take a deep breath and duplicate the Scene. Now edit the copied Scene (duplicated, not referenced Sources, other than maybe camera presuming not playing with filters, etc) in Preview Window. Once happy, now make that Live. There is more nuanced approaches, but try this to start