config

export default {
name: 'MyComponent',
methods: {
track () {
this.$gtag.config({
'cookie_prefix': 'MyCookie',
'cookie_domain': 'blog.example.com',
'cookie_expires': 28 * 24 * 60 * 60
})
}
}
}

Remember, this is just an example. check the all API parameters in the official gtag documentation here