Welcome! I’m sure there are several ways to do this, but one easy way would be:
One) create a virtual switch for each of the modes you want to have on the cube.
Once you’ve created the switch, it will show up on your list of switches just like your physical devices, so you can select it from a routine or a smartapp.
- use the “switch changes mode” Smart app that is available in the marketplace section of the mobile app to have each switch assigned to a specific mode
Three) build the mood cube as usual and instead of having it turn on physical lights you have it turn on those virtual switches.
So, straightforward and easy, but obviously a lot of steps. I’m sure there’s a fancy way to do it with some other smart app, this was just the first one that occurred to me. 
Changing modes manually
As far as your general question, it sounds like a good way to change modes to me. There are a lot of people who change modes manually for specific use cases, more typically by using the button on a minimote, but there’s no reason not to use the mood cube for it.
For example, there is a motion sensor in the bedroom at my house. During the day when the mode is “home” that sensor is ignored completely. At sunset, the mode automatically changes to “night” with a routine. Then if the motion sensor is triggered, the overhead ceiling light comes on. At night when I am ready to go to bed, I manually change the mode to “asleep.” When the mode is “asleep,” the motion sensor being triggered does not turn on the overhead ceiling light – – instead it turns on a soft nightlight. Then the next morning at 7 AM a different routine changes the mode back to home.
So two timebased mode changes, and one that I change manually.