how to extend the catalog?

Hi,

I want to extend the catalog, i think the key is
pg_attribute.h, pg_class.h, pg_type.h

is it enough:

1. add pg_xxx.h 
2.modify pg_attribute.h, pg_class.h, pg_type.h, catname.h,   indexing.h, indexing.c, Makefile

i tried once, it was ok when target to template. but like a mess
when target to global.

what is the thing.