Not quite: it seems that at each level up you have a chance for an extra stat increase. This chance is determined by the metal type. If you change the metal type at a higher level, for each level it the stat increase is determined and added up, using the probability dictated by the new metal type.
That means that if you use a Titanium shard on an Iron beast not all stats would go up 54 points, but on average the increase would be close to that. Some stats will increase more, others less – it’s a matter of chance. If you increase metal quality only slightly, say from iron to copper, some stats may even go down. Also, you can have a ‘good roll’, meaning that your average increase is above 54 per stat, or a ‘bad roll’, meaning that the average increase is lower than the expected 54. At least that’s my understanding based on discussion with other players, reading in forums, and doing my own testing.