The wheelhouses have been taken off so the ships could be transferred from the Lobith yard to Foxhol through inland waters.
For info about the future use of the ships and a render see here: https://www.dehoop.net/news/ (msg from 12/2/'19)

Ship Name HOOP LOBITH 459 Shiptype Crew/Supply Vessel
IMO/LR No. 9731303 Gross 493
Call Sign Deadweight 210
MMSI No. Year of Build 2019
Flag Mexico Status Launched
Operator Oceanografia SA de CV Shipbuilder De Hoop Lobith


Ship Name HOOP LOBITH 457 Shiptype Crew/Supply Vessel
IMO/LR No. 9731286 Gross 493
Call Sign Deadweight 210
MMSI No. Year of Build 2019
Flag Mexico Status Launched
Operator Oceanografia SA de CV Shipbuilder De Hoop Lobith

According Lloyds date base.

I think that they are the other way round,
457 - 9731286 on the right still in the blue colours seen in 2017
http://www.shipspotting.com/gallery/photo.php?lid=2672003

459 on the left, now repainted from the black/white colours seen here in 2014
http://www.shipspotting.com/gallery/photo.php?lid=2304032

Note that previous wheelhouses have been removed.

Special Mission Vessel? Who will be operating them? An what will their task be. Just curious.

YN 457 = IMO 9731286
YN 459 = IMO 9731303