You can try the tool "EditContacts":

http://www.marchert.de/software.html#ec

It`s still a beta version but should work fine. English help is not
avaiable at this time however.

To change the message class select on the tab "Settings" the checkbox
"All" and then select the filed "Message Class". Now a hint appears to
confirm reading all existing message classes in Outlook.

After that you can choose in the lists your desiered message class and
replace or overwrite the existing class.

Peter

--
Peter Marchert
[EDP-Service Marchert]
Homepage: http://www.marchert.de
Programming for Excel and Outlook


On 10 Feb., 13:39, Stephen Morgan wrote:
I have created a custom Contacts Form and saved it in my Personal Forms
Library, and it is also the default Form when I create a new Contact.
Now I want to change all the old Contacts to now show my new Form, and I
understand I need to change its Message Class from IPM.Contacts to
IPM.Contacts.My Design where "My Design" is the name of my new Form.
I've run "DocMessageClass" Version 1.0 - whilst it change the class to
my new form, when I click an old contact, the new form does not show.
Any hints please?