Hi R G, in case of MB51, you can set this report in cuztomizing in SPRO-->F5-->Materials Management-->Inventory Management and Physical Inventory-->Reporting-->Define Field Selection for Material Document List
In this way you can set if any field of MKPF or MSEG Table to show on Selection Screen or on Output Field, and you can set blank on the check mark "Output field" for the field MSEG EXBWR Externally Entered Posting Amount in Local Currency, and the MB51 not show this field again but any user.
In other hand maybe you check with a BASIS the Authority Checks of Transactions in SU24 and maybe have a chance to block that type information.