According to this Facebook post (link) MRCE ER20-003 has arrived at the workshop in Ljubljana. Here it will receive the Slovenian service number 645 003.

It has been confirmed that the locomotive is hired to SZ, which will homologate the locomotive for the Slovenian network. Because the Slovenian network still suffers from problems with overhead wiring, additional diesel locomotives are rented to assist electric locomotives on part of the network where the overhead wiring is not functioning.

(MRCE)