IDA Help: apply_type

Apply the specified type to the address
     ea    - the address of the object
     type  - typeinfo object or a C declaration string with ';'
             if specified as zero or an empty string, then the type
             assciated with 'ea' will be deleted
     flags - combination of TINFO_... constants or 0
returns: 1-ok, 0-failed.
Note: this function accepts member ids and change struct member types too

success apply_type(long ea, typeinfo type, long flags = TINFO_DEFINITE);

#define TINFO_GUESSED    0x0000 // this is a guessed type
#define TINFO_DEFINITE   0x0001 // this is a definite type
#define TINFO_DELAYFUNC  0x0002 // if type is a function and no function exists at ea,
                                // schedule its creation and argument renaming to auto-analysis
                                // otherwise try to create it immediately