I currently don't understand how I can save v, as what data type and resulting from that how to loop over the nodes from any stored variable.https://forum.ansys.com/discussion/comment/109657#Comment_109657

You will not be saving v. it is an object, you can save numbers.nSave integer corresponding to the face order after sorting. Now when you loop, read this integer and you know where is the face. The idea behind this is that they are not called in order, nor by the same node.nExample ... when looping, the Node takes face X. Then it reads F_UDMI for this face, it finds 10. Now it should apply the equation to position Node 10. The order now doesn't matter as you have the order stored the UDMIn