I found 2 ways to achieve what you want, but I have not seen a difference between the 2 methods yet.

In either method, to get “unapplied” you simply need to select the native field “Amount Remaining” in the results, better yet you can also add “Amount Remaining is above 0 ” flag to your criterias and set to true if you want only those Credit Memos with a unapplied value to come out.

For “applied”:

Method #1

Use native field ” Applied To Link Amount ” ,  although I have not seen if this is valid for Credit Memos that are partly applied to more than 2 invoices…

Method  #2

Add a calculated result row ” Formula (Currency) ” and in the formula field, add up the following 2 native fields:  {amount}+{amountremaining}
Remember to add them up as Amount for a credit memo is negative while the amount remaining is a positive value. I gave this calculated row a custom label <Amount Applied>

Hope this helps

Based on a SuiteAnswers article I found, this is a recommended method. [SS1.x] Pass a Value from the Before Submit to the After Submit Script

I tested the code myself and as @michoel pointed out about the not guaranteed TTL, this SESSION method does not have a TTL.

var sessionObj = runtime.getCurrentSession();
 
sessionObj.set({
name: "myKey",
value: "myValue"
});
 
log.debug("Session object myKey value: " + sessionObj.get({name: "myKey"});