Handling actions of guest and authorized user android

Question

I have an app with registration/login and guest mode. User can choose his way on the registration/login screen (enter his phone number or click on "as guest" button). Difference between this two modes is that when guest clicking on some buttons app should show him dialog "u have to be authorized" with some buttons.

So the question what is the best way to handle this ? Maybe any design pattern ?

"If" looks like very dirty way, so im trying to find something better.