Yes, this can be done. Here's what I would do...
Add a Branch node and use regular expressions to read the subject line and make a determination if it requires a subject line change. So if the subject line has the customers ESSN, you'll probably want to have several conditions, one for each country in the EU. So if we take Belgium, which is 11 digits long without spaces or delimiters, your condition tab should have something like this...
Object: Email
Attribute: Subject
Operator: Matches
Value: [0-9]{11}
The [0-9]{11} is the regular expression. Now if there are spaces or delimiters, you would have to modify your regular expression.
If the condition is TRUE, go to the TRUE tab and what I would do is the following:
Object: Activity
Name: Description
Type: Constant
Value: GDPR (This can be whatever you want it to be)
So we can now route emails to a different node in the workflow based on whether or not the condition has been met. The true branch of the Branch node will then go to a Modify Object node, and the false branch will go to wherever you need it to go.
In the Modify Object node, Make sure to select on the Condition tab This rule is always true. Over on the True tab...
Object: Email
Name: Subject
Type: Constant
Value: (whatever you want)
So the Branch Node helps you identity which emails should have its subject changed, and the Modify Object node does the actual changing of the subject line.
