OB08 shows Client has status 'not modifiable'

Hello,

When I'm trying to maintain Exchange rate through T code OB08 in quality client, it shows a message as "Client has status 'not modifiable" , later basis administrator has opened the client,and now it is modifiable. But, since he has opened the client,the customising settings are also showing as editable in quality client.

I wanted to restrict only the T code OB08 as modifiable and spro settings has to show the same message "Client has status 'not modifiable".

Please advise.

Thanks & Regards

Ramesh Nair