Is possible modify the table RDB$USER_PRIVILEGES directy.

I like agregate the privileges from roles to user, example, is possible
this (is a dirty e imcomplete sentence of example):

Variables:
user: User to grant the privileges
role: Role from suply the privileges

insert into RDB$USER_PRIVILEGES (RDB$USER, RDB$GRANTOR, RDB$PRIVILEGE,
RDB$GRANT_OPTION, RDB$RELATION_NAME, RDB$FIELD_NAME, RDB$USER_TYPE,
RDB$OBJECT_TYPE)
select :user, RDB$GRANTOR, RDB$PRIVILEGE, NULL, RDB$RELATION_NAME,
RDB$FIELD_NAME, 8, 0
from RDB$USER_PRIVILEGES
where (RDB$USER_PRIVILEGES = :role)



This system + 2 tables:

TS_USER
USER

TS_ROLES
USER
ROLE

Permit a system for manager privileges for user in the database baseed
in rights of roles:

Example of "possible" (not testing) store procedure:

Variables:
user: User to grant the privileges


delete from RDB$USER_PRIVILEGES
where RDB$USER = :user;

insert into RDB$USER_PRIVILEGES (RDB$USER, RDB$GRANTOR, RDB$PRIVILEGE,
RDB$GRANT_OPTION, RDB$RELATION_NAME, RDB$FIELD_NAME, RDB$USER_TYPE,
RDB$OBJECT_TYPE)
select distinct :user, RDB$GRANTOR, RDB$PRIVILEGE, NULL,
RDB$RELATION_NAME, RDB$FIELD_NAME, 8, 0
from RDB$USER_PRIVILEGES
where RDB$USER_PRIVILEGES in (select((select ROLE from TS_ROLES where
USER = :user) union ('PUBLICO')));


Distinct for delete the same rights for several roles.

The table TS_USER is necesary for work why a role PUBLIC ("PUBLICO")
private for the specific database.
The rights for roles are manager normally.

For this system is necesary can modify the table RDB$USER_PRIVILEGES
directy. Is possible??

Un Saludo;
Antonio Muñoz

P.D. Perdón por mi mal inglés