Hi Vincenzo,
Yes, you can create custom attributes for your users and these attributes can be added into the SAML2 assertion. You can find more information here:
API - https://help.hana.ondemand.com/cloud_identity/frameset.htm?e6bb70d5e43c4ff89ff700beb82b25fe.html
User Import - https://help.hana.ondemand.com/cloud_identity/frameset.htm?33838e0760f8411daf758a1c11818cc4.html
I think that for your scenario it will be better to use User Groups - that is our latest feature - https://help.hana.ondemand.com/cloud_identity/frameset.htm?de21efe39e1442618388784891497067.html
For more information about User Groups and how to assign to a user you can check this page https://help.hana.ondemand.com/cloud_identity/frameset.htm?ddd067c899f94e2f9006cc4dd417be80.html
Best Regards,
Valentin