Custom Magic Weapon Proficiency

[Caedhros]

I have created a custom weapon I am trying to code. (flametongue rapier with increased damage - d12 instead of d8) It all works except proficiency.

If I list "simple" as the proficiency damage etc displays as intended (as the character wielding it has simple proficiency). However, the rapier is the only martial weapon he is proficient with, so it obviously doesn't work if I list marital proficiency as required. (I'll leave it this way if I can't figure it out because it works for now...on this character.)

If I Gizmo-bootstrap it as a rapier, then proficiency is right but the weapon only shows damage as a flametongue rapier and the custom increased damage is ignored (1d8 shows instead of 1d12). I want to set a special proficiency somehow (requiring only proficiency, rapier) but I don't see how to do that. I can select "special" under proficiency required, but I haven't figured out how to specify WHICH proficiency the weapon requires.

I call upon the smart person collective for guidance. Thank you!