Some 3D printers are made for modification, such as the RepRap kits or early MakerBots. But some 3D printers were specifically designed to be used "out of the box" without modification. These 3D printers were not designed for modification by ingenious owners.
However, in spite of such design constraints, we see continuing effort by inventive 3D printer owners to mod their 3D printers. Take the venerable BFB 3000 3D printer, originally marketed a few years ago and still owned by many. It was designed as a complete, no-need-to-modify unit. But here's several ways to enhance it:
Install a glass bed, suitable for experimentation with heated bed function.
Install a heating element, if you've got a glass bed (see above). This enhancement would dramatically reduce bottom warping on your ABS plastic prints.
If you're in a rush to install a heated bed system, you can purchase the entire system at once, including power supply, bed and heating element.
To see your prints better, consider installing a rack of LED lights along to top edge.
Even if your 3D printer is not designed for modification - do it anyway!