Sandboxie provides a safe way to run apps by creating a self-contained, isolated environment in which a program runs - without ever touching your file system or registry. For example, if you run your web browser inside Sandboxie and you somehow contract a nasty bit of spyware, simply terminate the Sandboxed browser and delete the Sandbox - no more spyware!
Sandboxie is also very useful for testing apps - you can install a program inside a Sandbox, use it all you want, then close it and delete the Sandbox. The app will be gone, and no traces of it are left on your system.
While Sandboxie is a useful way to test-install apps, it is not easy to view the reg hive created inside the sandbox in order to monitor what the installation process has added to Sandboxie's virtual registry (and therefore what the installation would add to your registry if you were to run it outside of Sandboxie). By using a second program called RegFromApp, we are able to view all registry entries written to Sandboxie's virtual registry system while running an installer.
Download RegFromApp here, and extract it to c:/program files/regfromapp/
This can be useful in other ways too. If you want to know what registry key is associated with a particular setting in an app, you can run that app using this code, then change the setting in question - any changes that the app tries to make to the registry are reflected immediately in RegFromApp. Further, because RegFromApp can export .reg files, you may be able to use them to make changes in apps or in windows by running .reg files with .bat files - meaning you can use DOpus to control these things easily.
Of course, this is all possible without the use of either Sandboxie or RegFromApp, but these two programs together let you explore different possibilities without making any actual changes to your system.
You don't need a 3rd-party-app to check the registry. If you have installed a program in a sandbox, simply rightclick on c:\windows\regedit.exe and select "Start with Sandboxie". Select your sandbox and RegEdit will show the correct registry-entries. Works here on W10 like a charm.
This does not seem related to Directory Opus, since it happens with or without Opus's involvement, so you should probably go to Sandboxie's forum for help with it.
RegFromApp and RegEdit do quite different things. But, again, this isn't really the right place to discuss them so let's leave it at that.