Rhino loads the .NET framework into it’s process and uses that to execute .NET code.
The version of the .NET framework that Rhino loads is the most recent 4.x version installed on a computer. The Rhino 6 installer makes sure that at least .NET 4.5 is installed on the user’s computer. You can use 4.7.2 features, but then you will need to make sure that 4.7.2 is installed on the user’s computer.