A drill will cause the plastic to crack. You need to use a dremel tool with the proper bit if you want to prevent this sort of problem. I was In your shoes and did this DIY a few months back. Here is my negative feedback:
1. Need to take apart housings to remove dust after holes are made
2. Time consuming
3. Had to use my friends dremel tool
4. He didn't have the right bit
5. The outcome was not worth it
6. The yellow bulbs I used did not look good IMO
I wish I never did this project. But I will admit, the DIY thread convinced me.