Anything That You Find In SQL Object Scripts, You Can Also Find Them In System Tables?

I tried all the INFORMATION_SCHEMA on SQL 2000 and
I see that the system tables hold pretty much everything I am
interested in: Objects names (columns, functions, stored procedures, ...)
stored procedure statements in syscomments table.

My questions are:

If you script your whole database everything you end up having
in the text sql scripts, are those also located in the system tables?
That means i could simply read those system tables to get any information
I would normally look in the sql script files?

Can i quickly generate a SQL statement of all the indexes on my database?

I read many places that Microsoft
says not to modify anything in those tables and not query them since their
structure might change in future SQL versions.

Is it safe to use and rely the system tables?

I basically want to do at least fetching of information i want from the
system tables rather than the SQL script files.
I also want to know if it's pretty safe for me to make changes in these
tables.
Can i rename an object name for example an Index name, a Stored Procedure
name?
Can i add a new column in the syscolumns table for a user table?

Thank you