Hi @reaOSGF,
Thanks for reaching out! While others in the community may have more advice to offer, I did want to mention that we do not support adding additional fields to the data model. To maintain consistency between all Specify installations, we encourage all users to change the field caption for an existing field instead!
Would using a field like text1 on the Accession table as a second identifier work in your use case? In the Specify 7.9.3 update we also introduced uniqueness rules configuration so you can have the field be unique at a given level (collection, discipline, division, etc).
Depending on your workflow, you can have the other database interact with and treat text1 (or any required fields) as a dedicated field for your purposes.
I’d be interested to hear from the community as well on what advice/experience they have with interactions like the one you are looking to configure!