c_lexer.py module has a tuple "keywords" definition. New keywords can be added to the existing list. Make sure the new keywords are accounted for in syntax rules defined in c_parser.py. For example, if a new type "mytype_t" has been added to the keywords, it has to be also added to the p_type_specifier function doc string in order to extend definition of the "type_specifier" as shown in the following example:
def p_type_specifier_1(self, p):
""" type_specifier : VOID
| BOOL
| CHAR
| MYTYPE_T
...
Same approach works for other types of keywords.