Hi Kim,
Two things that might give you trouble:
1. I don’t know how well the plastic will tolerate the heat of the resin curing. If you want to try, I would cast it somewhere you can easily capture a mess should the resin eat through the plastic.
2. A mold release is definitely necessary for casting in this. Even then, I don’t know if you will be able to get it out. You can see what happened when I tried casting resin in a thin plastic soap mold: https://resinobsession.com/molds-mold-making/casting-resin-in-a-soap-mold
As for what you can do with it, I can see it being a neat looking light pull. You could also try drilling it so that you could use it to string lights. Imagine drilling horizontally through the base, then drilling perpendicular to that up through the bulb. Maybe then you could pass Christmas tree lights through them to help light them up. If you are only casting a ‘half’ light bulb, you could put a light behind it.