I'm not going to answer if it's possible to change your rigid fork, instead i'll answer why its not a good idea.
Firstly with the exception of the odd teenager running high on adrenaline no-one is riding their bike in a city in a manner where a suspension fork makes any difference. The primary purpose of a suspension fork isn't for comfort, it is to keep the wheel tracking the ground for grip/safety. The secondary purpose is to absorb impacts, but generally much bigger impacts than you would find in a city.
Short travel suspension forks are designed for situations in the pictures below rather than a kerb or patch of broken tarmac:
The second reason is that suspension forks typically found on hybrid/town bikes are typically very bad quality. They are generally either so stiff they do nothing or so soft they bounce endlessly wasting energy. They lack adjustment features or high tech coatings and often have uppers that are too narrow and flexy.
For the type of impact typically found in town/city riding and the fact this type of rider is usually looking for comfort there are other areas that can give much better results such as wider tyres at lower pressure and softer grips.
Finally, you can learn to mitigate many of the impacts you will find in town/city riding. By altering your weight distribution on the bike you can very much reduce impacts felt through the bars.