Is there a way to define a Monitor Point in CFX-Pre based on its node number and then track a variable at this node?
Yes, it is possible to do this. There's a CCL only feature that allows you to attach a Monitor Point to a particular node. It is a beta feature in version 11.0. The CCL is:
MONITOR POINT: Monitor Point 1
Domain Name = Domain 1
Option = Vertex in Domain
Vertex Number = 84634
Output Variables List = Total Mesh Displacement
The Domain Name obviously needs to match the name of the domain of interest. The variable of interest will often be Total Mesh Displacement, which will allow you to track the magnitude of the displacement of the selected node, but any variable can be entered.
To find out a vertex (node) number at the point of interest, you can load the definition (.def) file into CFX-Post and then create a Point at the required XYZ location. After creating the Point, the nearest node number will be listed on the Geometry tab for the Point. If you don't see this information then move the point slightly so that it lies within the mesh volume rather than on the mesh boundary.