setting the map to 850 effectively turn off egr
No not really, it just closes the EGR-value, but all controls and error detections are still active.
To turn off EGR, you need to turn off the EGR control, what, at the end, is as easy, as setting the EGR-AirMass-SetValue map to 850mg/h.
The problem with your solution:
you set expacted airmass to 850mg/h, but the engine is only able to promoto about 400 to 500mg/h without boost. The allowed differenz is 100 to 180mg/h, between 1500 and 1800rpm.
So, you will get DTC, when you drive in this engine range at low load..