Changing subkeys: what impact does it have?

[Faramir]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hello!
      If I make 1 subkey for signing, and another one for encryption,
and after a while I delete them and make a new subkey's pair, would I be
able to read messages encrypted to me with the old pair? Does my public
key change when I add or delete a subkey?

      thanks...
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iQEcBAEBAgAGBQJILE/+AAoJEIISGkVDGUEOm5AH/37uQOtwZWm4jaf36aYpk9d0
KahJUsj1JBnVmK+cDB0EW84qIpe3eUyS9Z6djgrm+3fE6VMoe9dpmy2y9SwGgiff
sp+oY7RRuf+NJoKvXwFlQgM6UbELj9c4bSJr3KDBc2uzRHriQNVxRQA+JnVl8n6M
DihnCXWc7xP4DyAHe4FwC8PhRx7ok4791/Zwq5CjdnNWG5A/1A9QPP/pQBsDxKH9
iT2EZfBMfcbG6wwd10o2iUTk/zZhSOEwRVAqHJQZyi3c7AHq/T+/C9ZuB/iJrEoD
mFQ5VCWinVfGKW5oeyeb6EE+r/mG6yWLPTNKmqUQQBROadjtyvbzse68LavGufs=
=WmJW
-----END PGP SIGNATURE-----