I don't know. And although you can legitimately fit a Mk3 interstitial plus a faceplate you cannot legitimately replace the wall unit. Which is what you would have to do to get rid of a Mk4.
I would be fitting a Mk3 + faceplate, (you may still have your original faceplate from pre-XTE-2005), and resisting a Mk4 replacing it. As it would be "BT" kit the engineer is less likely to insist than with the XTE-2005.
Maybe Zarjaz knows.
Edit - AIUI if they replace a master socket whilst visiting for some other purpose that itself is free. Though the visit may or may not be depending on the callout. To me, that would be another reason to remove the XTE-2005 first, so that cannot be blamed for the problem.
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Edited by RobertoS (Thu 30-Mar-17 01:08:47)