I recommend looking into org-edna
(http://www.nongnu.org/org-edna-el/#conditional_forms).
You can try to use "has-property" in combination with "set-property" as
a TRIGGER.
Alternatively, you can customize org-property-changed-functions (see
Is there a way to set properties using other properties? Doesn't matter
if its on export only, though it would be nice to have it in-situ.
here's an example (obviously doesn't work), where a project properties
for the project client only needs the CLIENT property filled, the rest
of it
