When you update and save a server message in the message editor window, you are prompted to preserve the client message.

If you click Yes on the Preserve Client Message Changes message box, the changes that were manually applied to the fields in a client message are preserved. This action indicates that the AccessType and DataType properties of the field are not changed. Otherwise, the new information from the updated server message overwrites the field properties.

If you click No, the existing client message will be overwritten.