I am using a SET node to store a few global variables that I would like to then have updated at some point further down in the workflow. How do I access that SET node in a function item node (or other?) so that I may change the value of the items in the SET node?
Welcome to the community @n8nUser!
Not sure I understand. You can not change the value on the SET node after it did execute (even if you could it would not matter as the node did already execute). You can access however the output data of the node with
$node as documented here:
And if you want to change the data in the flow to a new value you can do that by using another SET node.