As a workaround you can temporary disable extension in Extension Manager or if you have a SketchUcation ExtensionStore installed you can use it for similar purpose.
You need to restart SU to take effect of disabling for most of the extension.
If you use the Sketchucation Extension Store Tool you can either disable extensions and only temporarily install them when you want them…
…and you can create sets that can be loaded or not as desired.