I wrote this one not realizing there is already a plugin which offers simular functionality, Camaleón. None-the-less I will release mine as well as an alternative. This is functionality I wanted for a while so coded to my needs.
What this plugin does is cycle through a set of themes you configure. Use Super+Alt+0 to cycle up and Super+Alt+9 to cycle down (please let me know if this shortcut conflicts with anything Windows or Linux).
By default it will cycle through all the default themes but you really should go to "Preferences -> Package Settings -> QuickThemes -> Settings - User" and set it up for just the themes you use regularly.
I set it my config up for three: One muted, one high-contrast, and one bright so I can work in all environments and lighting conditions.