Our bike's plastic is fairly durable and strong, but oopsies happen. I recently rebuilt a 2004 that had a lot of oopsies on it. A lot of broken and cracked plastic, including two completely broken tabs for the top shelter the previous owner wire tied (literally, copper wire tied the shelter to the radiator side panel).
So anyhow, get yourself a small baby food jar or similar, and some ABS panels. I bought a couple of panels on eBay for ~ $10. And get some MEK (mono ethyl ketone). Cut up some ABS, toss in with a bit of MEK and let it sit overnight. You'll end up with a nice spreadable/paintable mixture. If too runny, leave the lid off for a bit.
Now for small repairs, put some painters tape on the backside and paint away. For filler material if needed use a bit of the ABS plastic. Let dry overnight for full strength.
If need to make a tab or panel piece that requires shaping, use leather gloves and a hot air gun. The bike I worked on had massive cracking around both antenna mounts on the trunk. Cut ABS panel to size, heated and shaped, then used the ABS slurry like glue and clamped the panel. Tape on the outside to prevent run-thru. Use a step drill to make the mounting holes, you have to actually look to see what was previously large cracks. In