IDA Help: create_custom_data

Convert the current item to a custom data type
     ea   - linear address
     size - size of the item
     dtid - custom data type id (see find_custom_data_type)
     fid  - custom data format id (see find_custom_data_format)
returns: 1-ok, 0-failure
This is a convenience macro, see also create_data() function

#define create_custom_data(ea, size, dtid, fid) create_data(ea, FF_CUSTOM, size, dtid|((fid)<<16))