I have successfully re-compiled Godot 2.1 with my added script encryption key as well as the Windows 32-bit export template too. Now how do I compile the export templates for Linux and OSX while using Windows 10?
I don't think Windows has an appropriate toolchain for that.
You'd have to either dual boot a Linux system to cross-compile the Linux and OSX templates from there, or maybe try it in a virtual machine (e.g. VirtualBox).
Right, I'll try the virtual machine approach.