I recently needed this functionality to hide some of my platforms in LaunchBox without wanting to remove them entirely. I set up an arcade cabinet at home running on LaunchBox and I only wanted to keep the MAME platform visible, but I really didn't want to have to delete all my other platforms just in case I want to play them again.
So I ended up writing it in my little homebrew ROMs manager application, and it looks something like this;
If anyone else needs this functionality (full source code is available), you can download the DROMsM setup.exe from https://github.com/dreasgrech/DROMsM/releases
The tool is accessible from Tools -> LaunchBox -> Manage Platforms
---
To keep track of your platforms, LaunchBox keeps a set of XML files in the Data/Platforms directory and it seems like LaunchBox ignores platform files that do not have the XML extension, so what the tool does is change the extension of the platform you want hidden to .hidden instead of .xml.
From the tool itself, you can both show or hide platforms where one option would set the file extension to .xml and the other to .hidden.
You can also bulk show/hide all your platforms in one operation.
This will allow you to hide entire LaunchBox platforms without losing the functionality of hiding specific games.