I believe you would be using multiple modules to create various resources(EC2,ELB, Etc) in AWS using Terraform. You can create a custom module having output value of each variable you want to configure per your requirement like aws-region, etc. Then source(import) this custom module into your resource module and use its values using $.

custom_module

    output "aws_region" {
      value = "us-xyz-1"
    }
    output "aws_anyproperty" {
      value = "abc"
    }
    
    Add above custom_module as source in your resource module
    
    module "custom_module" {
      source="../../../modules/custom_module"
    }
    
    provider "aws" {
      version="~> y.x"
      profile="${module.custom_module.aws_anyproperty}"
      region="${module.custom_module.aws_region}"
    }