What you call the "main perk" is actually called "archetype". The archetypes are for specific players and not interchangeable.
If you created a pitcher, you chose the type of pitcher you wanted when you created him. If you chose "Velocity", then you get velocity related archetypes (Filthy Cheese and Painted Cheese).
When you create a position player, you choose either Power, Contact or Fielding. Each of these would give you a different pair of archetypes.
Finally, if you create a two-way player, you choose a type of pitcher, for when you pitch, and a type of position player, when you bat. For example, if you chose Velocity pitching and Power hitting, your archetype is Cheesy Slugger.
In case you don't know, the names in archetypes come from the traits:
Velocity = Cheese
Break = Filth
Control = Paint
Power = Slugger
Contact = Sparking
Fielding = Slick (slickster)