Is it possible to change the date of your Mac so it is not system-wide, but only for certain applications? For example, changing the date to 15th June for VS Code & Firefox, but not Google Chrome, etc.
I am on an M1 MacBook Air, Monterey 12.5
No, this is not possible.
You could achieve the desired behaviour by running the applications within a virtual machine whose internal date has been changed. You would also need to isolate the virtual machine from the network to stop macOS fetching the time remotely.
I created a script to solve this specific problem and then converted it into a shortcut to automate the process. Instead of manually running the script and entering a password each time, the shortcut can now launch the app automatically. The shortcut and instructions are available on a GitHub repository. Here you go : https://github.com/ArunyaGoojar/RunAsDate-for-MacOS