Hi Peter,
Yes, You can use the constants in the microflows for that firstly you need to create the constant in the modeler.
let me give an example how I used a constant firstly I created a constant and I need to showcase a text with particular color so I created a color constant and mapped that color constant in the microflow change activity to the particular member of the object use ‘@example.colorBlue’
Hope this helps.
You can refer to a constant in an expression by starting with @ and then the name of the constant.
Please note that for the app it's considered a constant as the app can't change the value, but you can change it using configurations, or setting the value in the cloud portal.