If you have a hero level saber, you can change the color but just programming the SD card with the right options. As for physically changing out the LED, that is not a customer serviceable part on a thin-neck saber like the Prodigal Son. The emitter is bonded to the grenade section with a non-permanent version of Loc-Tite, and breaking that seal would void your warranty. If you bought an extra LED, you might consider keeping it for your next saber that can be configured with Quick-Connects that allow for easy swap-out of the LED.
As I said, if you want green, just program the SD card with the right configuration, and green you will have. If you require further instructions on Hero Level configuration, I believe there is information along those lines to be found in this forum, but I would have to search a little to point you there specifically. Hopefully, our other helpful members will see this, and help me out here.