How to Grey out the field "tracking number" during change mode in the order

HI Expert,

How to grey out the Tracking number (AFVGD-BEDNR) at Order -> Operation tab -> external tab ->tracking number.

during creation IW31 = not grey out and allow entry.

for change mode IW32 = grey out

if i set grey out at config OIOPD, it will grey out even during creation mode.

Please advise

Thanks

Regards