How can I change my dialer setting conditionally I use my google voice number for almost anything but things that won't accept a VoIP number for registration and account recovery and I give it to them, for a good reason. 

So, my default dialer setting is "Ask me every time I place a call". I am mostly happy with the setting since an extra click on the screen is not that big of a deal. Except when I am in my car and trying to dial a number using voice dialing. At which time I have fumble with the phone to click the right position on the screen to place my call. 

What I want is, as soon as my phone enters the PAN (personal area network) of my car's audio system (i.e. connects to car stereo using bluetooth) I want my dialer to default to google voice. And revert this setting back when I leave the car and disconnect from the stereo system.

How can I accomplish this ?

EDIT: If need be

OS: Android Nougat 

Phone : Motorola Nexus 6
I am vaguely familiar with Google Voice but let me see if I can help...

I dont believe that there is a way to change that setting when you hook up to certain devices. It also depends on what software (like Android Auto) you are using. Maybe through there it will let you change that but otherwise I am afraid that the answer in no. 

Hope that helps!