If the user follows the same naming convention as Veeva Message, do customized Messages get overwritten during system upgrading?
Yes. If using the Veeva naming convention for the External ID, these messages are overwritten.
When the user clones Veeva Messages, user naming conventions, such as adding the company abbreviation to the External ID (<Category>-<Name>-<Company Abbreviation>-<Language>), makes the cloned Veeva Message active. The Veeva original message is inactive for the same language.
As long as the External IDs are different, Veeva does not overwrite them.
CRM Help Documentation: Veeva Messages