I think you should avoid that as much as you can because that's not standard.
As for example... "SN's" displayname should be "Last Name", not "FirstName".
According to standard... "Givenname's" displayname is "FirstName".
In Gluu, we try to follow standard developed by consortiums and foundations / boards.
Now, you can try to follow w/e SPs want but that will place your IDP in a highly customized/non-standard position which you could easily avoid to just say 'no' sometimes to SPs. :-)
But, if there is no other way and you have to modify something in IDP... that's even possible. Please check the integration sections from our doc, [webex](https://www.gluu.org/docs/gluu-server/4.1/integration/saas/webex/) has such requirement.