Hello wals,
The phrase you used in your post 'before change it' made me answer that way. But we may have to go that way only in the absence of knowledge about means for authority check in IW32 initial screen. To achieve this, may be implicit enhancement in the program SAPLCOIH might be an answer.
Functionally this authorization is achieved through a ROLE assigned to users where an Authorization object I_TCODE restricts access.
Regards
KJogeswaraRao