There’s already some pawn variants.
The standard pawn
The 0-pawn (Berolina)
The 1-pawn (Soldier)
The Stone General (aka 2-pawn)
The 3-pawn (Sergeant)
Now for the fan-made ones: 4-pawn: replaces d-file and e-file pawns. Behaves like a normal pawn, but if you are Chinese, Japanese, or Korean, and you promoted it, then you lose.