I'd venture a guess that EEM applet is probably not up to the task due to the potential complexity of the custom "engineering rules". So, going down the path of using EEM Tcl policy (or policies), it seems on the XR, the "conf t" equivalent is "configure", which is the CLI pattern you want to intercept, or at least start "recording" at. Then upon detecting CLI input of either "end" or "configure", your script will either have already checked the configs entered so far line-by-line, stopping in place and warning the engineer if/when necessary, OR the script does the checking en masse at the "end" (no pun intended) by reading from the recorded configs saved in the Tcl's buffer or written to a file on the flash. If that's on the right track, I think the "Annotated TCL Script Example" on this page provides a rudimentary skeleton for this type of command interception & verification, via the line-by-line approach, which could make the script pretty big and unwieldy, depending on the complexity of your "engineering rules"
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/white_paper_c11-567132.html
The key words that I searched for was "Setting sync to yes enables the command to be executed, but the logic will really decide whether the command is ultimately permitted."
