Hi James,
You can insert a modification or an enhancement (whichever is applicable) in function module SO_OBJECT_INSERT. Field OBJLEN of the import parameter OBJECT_HD_CHANGE holds the file size value in bytes.
For your requirement, see below logic:
if OBJECT_HD_CHANGE-OBJLEN gt '000001000000'.
" error message and leave program
endif.
I suggest that you put your logic at the top part of the function module, before all the operations.
Regards,
Aldrin