This field can be maintained using transaction MASS_MARC, however you have to make a customising setting first. In customising transaction OMSR find the field WRPL-TRCOV and double-click. Remove the checkbox "Copy field content". Save.
Now in MASS_MARC you will find the Target Range of Cover field as the last field in the grid (or last field on the mass change dialog).
Thank you for your great advice!
I had to erase the flag for the field MARC-MAX_TROC in order to have the field in the mass change dialog (sap note 381942 was helpful). If the grid is shown in gray (not changable), it means that the WRPL record does not exist and cannot be changed.