Can force change the mass of an object? I have a difficulty in understanding this 'mass never changes'. Say, i punch/hit a ball until it deflates, or bursting a balloon with a needle - doesn't the mass of the ball/balloon change? the air already diffuses out from the ball. 
 A: Let's look at your system: a needle, a balloon skin, and a gas inside the skin. There is some total mass in this system.
Force of the needle pressed against the skin causes a stress which exceeds the strength of the skin material, making a hole. The air escapes through the hole after the force is gone, but the mass of the air doesn't change. The mass of the needle and the mass of the balloon skin don't change.
Force didn't make the mass of the system change. The mass of the system is  simply redistributed.  This would be the same as pulling apart a lump of clay and making two smaller lumps: the total mass is the same, but has been redistributed.
A: So in the beginning you have a plastic balloon that's not filled up. Let's say its mass of plastic is a number $k$. Then you fill the balloon with $1 g$ of air.
In the end you will have a balloon that weighs $k + 1g$ which is the mass of the plastic balloon plus the mass of air inside.
If you burst the balloon with a needle, the air will go out and you'll still end up with the same mass of plastic $k$. The mass of each of the components didn't change.
So, in Newtonian physics we say that mass never changes. This concept is particularly used when we want to calculate a force using Newton's formula: $F=m \cdot a$
A: The total mass of a system never changes, is a more clear way to think about it.  If you punch a balloon, air would come out of the balloon, but the total mass of the balloon before = the mass of the balloon after + the increase in the mass of the surrounding atmosphere (due to the extra air now being there).  The mass of the system stays constant.
The system includes the entire space where the piece(s) of the object in question end up or are involved.  So if you cut an apple in half and bring one half to the other side of the room, mass isn't somehow lost.  Sure each piece has less mass, but the mass of the entire system (in this case the room) remains constant.
If we could change / create mass, that would go against the Conservation of Mass / Conservation of Energy Law.  Although it would be nice, considering your electricity bill would decrease to 0  :)
A: in this case all the objects have individual masses and thus they form a system in which the mass of the object do not change
but in a microscopic subatomic system mass may change with respect to time
