You may reconfigure Undo to maintain more than 10 changes by adding the following .ini setting to your Teamstudio.ini file located in your Notes installation folders.
Add the following to your Teamstudio.ini:
Where xx is the number of undos to keep in the buffer, by default it is 10.
If you roll back the setting, i.e. from 20 to 10. This will cause Undo to trim excess changes back down to your configured setting.
Remember to restart your notes client after adding/removing the new .ini settings for changes to take effect.