importing new uid (offline master key setup)

[Matthew Monaco]

On my running system, I keep the public portions of the master key (certify
only) and subkey (combined encrypt and sign). I only keep the private portion of
the sub key.

Recently, I added a UID to the offline copy of my .gnupg directory. Importing
the UID into the pubring was simple enough, but I'm having trouble importing the
new UID into my secring.

Is this supported? Am I going to have the same problems if I change the
expiration date on either the master key or a subkey?

Thanks,
Matt