Occasionally, repository owners change related information, keys, etc. This
generally causes apt to issue an error to the user, such as:

...
Reading package lists... Done
E: Repository 'http://ppa.launchpad.net/<author>/<package>/ubuntu disco
InRelease' changed its 'Label' value from '<some old long label>' to '<some new
long label>'
N: This must be accepted explicitly before updates for this repository can be
applied. See apt-secure(8) manpage for details.
...

When using "apt" on the command line, the system asks:

Do you want to accept these changes and continue updating from this repository?
[y/N]

Synaptic will report the error, but does nothing to allow the user to accept
changes. The older "apt-get" tool does the same unless a --allow-releaseinfo-
change update" switch is given:

sudo apt-get --allow-releaseinfo-change update

I suggest an enhancement to allow synaptic to somehow "accept the changes" for
the affected repository(s).