I had tried some of the things for antenna mods nut none of them worked with the ever so slightly modified X9D+ SE... I decided to make my own, and after 3D printing 3 revisions have the design here... The Taranis X9D+ has had a mod you could do to allow for the fitment of a removable antenna. Well the SE has a removable antenna, but it's a small one that won't allow for the attachment of a larger (think long-range hack) antenna.
This allows for the larger antenna and has the notch created to fit the newer cases. Has been printed and tested on 2 different radios so I'm confident you'll have success with this.
Printed in PLA with basic settings from CURA.