You can very well!!
I am not sure if I understood your requirement, but here is what I have to say.
You have a copy book (say COPY01) with the following contents and you do NOT want C and D. I really do NOT understand why you do not want C and D!!
05 A PIC X(01).
05 B PIC X(01).
05 C PIC X(01).
05 D PIC X(01).
Then you can do something like.
01 REDF-RECORD REDEFINES WS-RECORD PIC X(02).
Now use REDF-RECORD instead of WS-RECORD.
If this is not what you are looking for, then clarify us on what you exactly want.