I have used a system for keeping the Mac App Store (MAS) version of Xcode alongside the latest Xcode beta that I thought might be worth sharing.

Firstly, I permit the MAS to install Xcode in its default location (/Applications).

I then create a folder called “Xcode betas” also under /Applications for the beta versions.

The trick so that the MAS does not upgrade/touch the wrong version of Xcode is to add this folder into the Spotlight Privacy tab like this:

Spotlight Privacy