Without changing the VST / VST3 folder?
You can remove the plugin paths in plugin manager (but only for vst2 I think)
Unfortunately not. If you don’t want to load them, the only one way would be to don’t activate this project.
Not sure why you ask, but if you’ve got a problem opening a project then you could try what I do. I have a reasonably important project which just crashes when I open it. So, I open another (v. small) project first, then I open the ‘problem’ project as a 2nd project and activate it when opening. It works then and opens fine. This is the only way I can open it. In terms of why it happens I can only say that its an old-ish project and was probably created a few years back on a previous Cb version.
Another thing I’ve had to do once is to email the project to someone who didn’t have the plugins that I thought were causing the problem. I asked on this forum in fact and someone stepped up. I sent them the bare project file, they opened it fine, removed the unavailable plugins and then saved and sent a new version back to me, which then opened fine on my system. Sorted.