CustomAction: how-to update a value of a field when executed.

CustomAction: how-to update a value of a field when executed.

Hi,
sorry if I ask a simple question but the manual/help, about that feature, seems not completed.

I want to launch from a view a custom action.
I need to send an email to the contacts of the selected list (simply to do), but I want also to *add* to the note field contents a detail, x all row, of the datestamp of executed command.

e.g expected result:

Name_Field===|====NOTES_FIELD=================|
Mr. Cannewson | Address checked; confirm email: sent on 5/5/2009;
-----------------------------------------------------------------------
Mr. John Levis   | Phone incorrect; confirm email: sent on 5/5/2009;
-----------------------------------------------------------------------
...
...

Where is in bold the added information about executed customaction.
May be is aesy... I hope...

Thank you,
Ago