For testing purposes if I connect red (live) wire on a position of black(neutral) wire that means if I interchange them, will there be any problems?
It depends.
As mentioned above, both conductors are considered "live" as they carry power, but under normal circumstances only the line (L) is at a voltage that is dangerous compared to that of the Earth around you.
I see your details say Tanzania and I do not know your electrical regulations, but assuming they are similar to the UK's due to historical connections then another factor has to be considered and that is the practice of only having fuses on the L path, and often only switching the L path.
As a result, while something like a light bulb won't care witch terminal is L and which is N, the reversal of the supply can result in a dangerous situation as the overload/fault protection of the fuse, and the means of isolation of the switch, are not removing the high voltage from the load. They are simply stopping the current from completing the loop for normal operations.
I.e. normally if you switch something off, or the fuse blows, then it has no L connection any more, but it still has N connected and is all internally at the N potential. This is close to the Earth in potential (as N is connected to the Earth back at your substation or similar point of supply) so relatively safe.
But if L & N are swapped, switching off make the load look "dead" as a light goes off, heater cools down, etc, but everything is now sitting at the L potential and so dangerous to touch or for any other fault.
So while the only difference between the L and N conductors in terms of
their physical construction is the colour of the insulation, they cannot be considered interchangeable electrically as under fault conditions the safety implications are quite different.
