Javascript and liquid markup on order success page in Shopify

I need to know how I add javascript and liquid markup on the order success page in Shopify using their API. It looks like I can't for a normal Shopify store (only Shopify Plus - possibly?). I know how to do this in the Shopify admin but this needs to be added as part of an app installation. Is there a different way I can do this?

This is all that I need to add:
var acTransaction = {
"user":[{
"email":"{{customer.email}}",
"firstname":"{{checkout.billing_address.first_name}}",
"lastname":"{{checkout.billing_address.last_name}}",
"order_id":"{{checkout.order_id}}",
"address":{
"address1":"{{checkout.billing_address.address1}}",
"address2":"{{checkout.billing_address.address2}}",
"address3":"",
"city":"{{checkout.billing_address.city}}",
"postcode":"{{checkout.billing_address.zip}}",
"country":"{{checkout.billing_address.country_code}}"}
}
],
"cart": [{"products":[
{% for line_item in line_items %}
{"id":"{{ line_item.sku }}","name":"{{ line_item.title }}","price":"{{ line_item.line_price | money_without_currency }}","quantity":{{ line_item.quantity }},"requires_av":{% if line_item.product.tags contains 'Requires AV' %}1{% else %}0{% endif %}
},
{% endfor %}
]}]
};