Triggers and System Tables.

Hello,
this is probably a really silly question, but where can i
control wether or not the superuser/root user can create a trigger
on a system table ?

Currently, have been tinkering with the idea of adding
in the ability to have 'session variables' for the connection, so
that before a transaction it can declare and save variables, so
that they can be used in the transaction themselves. This would
ease some problems i have with inheritance. It also would make
some sort of connection limiting per user a lot easier if it was
possible to attach triggers to pg_stat_activity (on INSERT only :)

So, the real question is, is this a question for hackers
mailing list or can anyone tell me how to drop the limitation ?

many thanks
Stef