It is indeed possible to replace the top trim of the tank, it's relatively inexpensive an there are lots of tools and instructions online you can use (I had a 30g breeder without the trim at all! So I've done some research on this hehe) however, it is quite time consuming. There are loads of tank lights you can find online and perhaps at a tee or aquarium store nearby that are specifically designed for tanks without the trim.
That is just a few options but will give you an idea of what to look for. Good luck!!!
2.5 gallon nano Snooki Sparkle
29 gallon community Yoyo, J-Wow, Jessica, Snape, Arnold, Nymeria, 6 Gold Neons (all "Goldie")