It can be done but is a royal PITA to get the trim and all the silicone off in order to bond your new bracing in place. building a glass tank is also not for beginners, more stories of failure than success. Acrylic is doable, especially if you have someone else cut all the pieces so they are nice and square with clean edges.
But you might be better off just buying a tank that was made the way you want it. If you wan't a glass tank (which I prefer for ease of cleaning anyhow) there are lots of places that can build you a rimless 40 breeder. Glass Cages comes to mind, I think they even stock one..........