IDA Help: set_storage_type

Set storage type
     start_ea - starting address
     end_ea   - ending address
     stt     - new storage type, one of STT_VA and STT_MM
returns: 0 - ok, otherwise internal error code

long set_storage_type(long start_ea, long end_ea, long stt);

#define STT_VA 0  // regular storage: virtual arrays, an explicit flag for each byte
#define STT_MM 1  // memory map: sparse storage. useful for huge objects