How to assign policies by updating ARM template?

nabi04 

Hi you can do that regarding the documentation below : 

Quickstart: New policy assignment with templates - Azure Policy | Microsoft Docs

But you will notice that resource group is always necessary and it will be scope .So if you need the subscription as scope you will be blocked .

If you don't want to do it through Github try Azure Blueprint it's more flexible 

Security compliance with Azure Policy and Azure Blueprints | Microsoft Docs

You can test this to see if it can fit your need : 

Go to Blueprints Menu 

https://portal.azure.com/#blade/Microsoft_Azure_Policy/BlueprintsMenuBlade/GetStarted 

Click Create 

Select Common Policies  ( You can also start with blank blueprint)

Give a name a description and a location (The management group or subscription where the blueprint is saved)

Click Next:Artifacts

click on ... and remove artifacts you don't want 

click add artifact  and choose Policy assignment as artifact type 

You will see all the iniative definitions and policy definitions 

select and add

click on save draft

In the notifications blade click on saving blueprint definition succeeded 

then publish blueprint  

Give a version and a change notes and hit publish 

Once published you can assign it by giving the necessary parameter values and click assign.