The virtual switches themselves only offer state values of on/off.
Normally in smartthings, you could have that switch going on be the trigger in a smartthings routine created in the smartthings app, and use it to change the “location mode“ to home or away. I’m not sure if that’s what you were trying to do or not, but it’s how it’s done in smartthings. There is a global variable for location mode. (there’s also one for security mode, by the way)
The following topic discusses more about that:
FAQ: Armed/Disarmed states vs Away/Home modes confusion
As it happens, it appears that this process has broken for local virtual devices yesterday. That bug is being discussed in the following thread. Note that things appear to still be working for virtual switches which run in the cloud. It’s only the local ones which are broken. But of course, that includes all of the ones from custom edge Drivers, like Vedge creator.
Local Virtual Switches and Location Modes Failing (15 Nov 2023)
So… we are not given the option to add more Available states for a Virtual switch. It’s just on or off.
There is a global variable called location mode which has the possible values of home or away, and you can change that based on the state of your virtual switch just by using a routine created in the smartthings app.
At least you could up until yesterday, when it appears to have broke. 
For your guest virtual device, you’ll just have to accept the state values of on or off. We don’t have a way to change what the values are called.