I used an Adafruit ESP32 and an Adafruit Neopixel Jewel to replace the hardware. The code was inspired by some of the projects on the CheerLights site.
The tree is 15+ years old and had been sitting in the closet for a few years. I decided this was the year to do something about it!
Thank you! There are a lot of fiber optic lamps out there now. If there's a Daiso in your neighborhood, they may have a little battery powered lamp for a couple of bucks or so. It's just big enough to put a Feather and a NeoPixel in.