Anurag,

There is no database migration from DB2 V8.1 to DB2 V8.2.
So all you to is flip your instance (the database doesn't care).
Now, once you have rebound you packages, if you want to go back you have
to rebind them again against the old system, not that DB2 picked up some
FP7 or FP9 smartness.
If you start using any of the new function you are committed of course.
If you drop and recreate SQL Procedures going from V8.1 to V8.2 you need
to redo that on the way back since the SQL Procedure architecture
changed (rebind is NOT good enough to pick up DB2 V8.2 SQL Procs btw. If
you want to benefit from V8.2 you need to drop/recreate)
Now the one thing I don't know is whether you can undo a call to
db2updv8 which updates your catalogs, but I suppose you should be able
to wait calling it until you're comfortable on FP11.
Depending on your level of paranoia you can do it one step at a time:
Upgrade the instance => test (downgrade up flipping the insance back)
Rebind => test (downgrade by flipping the instance and rebinding)
DROP/CREATE SQL procs => test (etc, etc...)
db2updv8 => test (dunno this one)

Cheers
Serge