Yes but also no. Combined magnets will act equivalent to a magnet of the combined size. Magnetic forces are also affected by the internals of the magnet (basically it pulls against itself) and this cancels out some of the magnetic pull. If the magnets are infinitely small then yes, adding a magnet will always increase the strength by the amount of magnets you add. But in the real world, 2 magnets will always be strictly less than twice as strong as 1 magnet. Small magnets this effect is not noticeable but strength will tapper off logarithmically as you add magnets depending on the strength density of the magnets. Really strong tiny magnets will loose strength per added magnet slower than big magnets of the same strength.