I think it´s not a good idea. I remember that Lupine 2009 offered a wider 18° lens for the Wilma Seoul P4 to replace the standard 15° lens. In your Wilma, there are other leds, and probably different height of the lens, so it will neither fit properly nor spread the light in a perfect way.
If I am correct, Lupine offered at that time the 19W Wilma with three different lenses 16 °/22 °/26° (with three different ledboards, 1200, 1300, 1500 lumen accordingly). Contact Lupine, it may be possible, that they have an older upgrade kit 16 °/22 °.
Another solution is to consider to buy the new upgrade kit to get additional 400 lumen to your current 19W Wilma (I use my Wilma also for Orientering (beside MTB), and a 26 degree lens suits me with the new 400 lumen upgrade).