When you are accessing properties of basic types, if you save them in a variable, you are basically making a copy of that property. For example, doing something like this does not make sense or do anything.
var node_name = get_node("Card/Name").text
node_name = card_name
When you do this, the variable "node_name" becomes a string, and on the second line you are overriding this temporary string to be some other string. The original node is unaffected.
You can instead do something like this:
var card_node = get_node("Card/Name")
card_node.text = card_name
Hope that helps.