Hi Vipra,
sounds a little bit silly to me.
Do not make a standard customizing, but modify a standard to suppress the message.
I'm not sure there could be a reasonable solution for unreasonable input.
For example, you can suppress this message in SRM, but you get no following documents in the backend with the same UOM.
Or you can try to suppress this message directly in backend, but, for exmaple, UOMs will not be sent in printed form for suppliert, and he can deliver 1 piece instead of 1 pack...
Regards
Konstantin