In Xubuntu, I can change the calendar display in the panel by using % labels – %A is the full weekday name, for instance. Is there any way to change this in Ubuntu Mate? The preference doesn’t allow it, and I tried used dconf but that didn’t work, either.
By the way, I am a confirmed Xubuntu user, but am very favorably impressed with this, especially for my notebook.
Use dconf-editor to navigate to /org/mate/panel/objects/clock/prefs you’ll find a key called custom-format. I’ll leave it as an exercise for the reader to figure out what that custom format should be 
If you figure it out please post the details here.
Thank you so much. I changed custom-format to the string I wanted – %A, %b. %d %l:%M %P – and then changed format from 24-hour to custom.
Thank you, additionally I found out, that these are strftime formatting variables: https://apidock.com/ruby/DateTime/strftime
My example use case (Day plus ISO8601 date plus time with seconds plus calendar week number):
%A, %F %T, KW%V
Tuesday, 2017-07-18 13:58:51, KW29
Just trying if some fancy formatting may be useful for daily work:
<small>%A, %Y-</small>%m-<b>%d</b> %T, <small>KW%V</small>
Tuesday, 2017-07-18 13:58:51, KW29