The short answer is: just try it, you are in for a lot of fun and puzzles.
If you have Windows nearby I would recommend Dolphin Smalltalk due to a great system browser.
> it's not only a code, it's a also current _state_ of the system
There is no difference in Smalltalk. The code includes all the created instances with current field values.
> updated code to a live system
From the user point of view everything is simple, yet the simplicity is the advantage of the compiler, not the user. If you update the code the instances that you upgrade run the new code, and if you don't upgrade the old objects they run the old code.
> it's not only a code, it's a also current _state_ of the system
There is no difference in Smalltalk. The code includes all the created instances with current field values.
> updated code to a live system
From the user point of view everything is simple, yet the simplicity is the advantage of the compiler, not the user. If you update the code the instances that you upgrade run the new code, and if you don't upgrade the old objects they run the old code.