One more question: is it possible to configure PT integration in a way that
that changes imported to PT are credited to the PT users corresponding to
Aha users who actually authored the original changes (matched based on
e-mail)?
Unfortunately, it isn't possible to directly query members by username or email address to extract their user ID. It would be necessary to get the person as part of a list using either the project membership or account membership endpoints (see https://www.pivotaltracker.com/help/api/rest/v5#Account_Memberships
or https://www.pivotaltracker.com/help/api/rest/v5#Project_Memberships).
it would be great if we could also assign by email address using a custom field.