If I understand correctly, you want to set the doc-level default of a Date-type attribute to be the current date-time? I see the intent but I think you are really describing (only some?) notes’ $PublicationDate to be whatever was current at the time of export.
At present, although the default for any Date-type attribute is "never’ (i.e. undefined [sic]), other date designator values cannot be used as a default. Nor (which) I’ve tested can you use action code such as
date("today") as a default. If you really want this, you may care to email support with a feature suggestion.
However, I think there is a simple solution as you state:
This is easily resolved in the export template. Lets assume it includes code such as ^value($PublicationDate)^ (or a formatted version thereof). Instead of:
At export, unless a note has a non-default value for $PublicationDate, it will instead insert the current date/time in default format. Of course, if you want a different format - e.g. locale short date only - then you’'d change: