Are you using the updates folder? did you make the changes to the planar_mill in there or in a custom enviroment?
If you have the option use latest templates then if the Update folder contains the same base option it will use that not the one in the templates location.
Hope this is of some help.
There are two locations that could have the same file in it the main location would be C:\Siemens\NX10\MACH\resource\template_part\metric
And the other is
If you changed the file in the main location this will be cancelled out as it will pull the one from the updates location unless you turn off use latest templates.
After you create an operation, go to Menu > Information > Part > Loaded Parts, and verify where the template part is located.
You should not modify files in the updates area - this is for Siemens to provide updated template and library files in a maintenance release or maintenance pack.
You should create a copy of the mill_planar template part and modify that. See these tech tip videow for one way to do this:
I would not rename the out of the box operations. Instead, copy and paste one, rename the copy, and change the template setting on the original so that it cannot be used as a template.