When I tinted my tail lights I played around with the idea of making the inner sections light up. I tried to pull them open using a heat gun but no dice. It looks like the housings are glued. I think I could fit a 194 bulb from the side on the top section, but it doesn't look like there is room on the bottom. I also am not sure on how the light would reflect since it isn't designed to be lit. I have 63k miles on my 18 limited hatch BTW so I don't mind some modifications, but I'd prefer it if I could find some cheap replacement housings to mess with before drilling into mine. If anyone knows where to find some let me know. I plan on looking into this further and will report back if I figure something out. Just found this on a Crosstrek forum
https://www.amazon.com/dp/B07FNL3F23/ref=cm_sw_r_cp_apa_i_yVicEbAQJM7SC
So it has been done, lm not sure about the strips though. Not a fan of the individual diode look. I wonder if these would fit. Should give a cleaner unbroken line look.https://www.amazon.com/dp/B07FNL3F23/ref=cm_sw_r_cp_apa_i_yVicEbAQJM7SC