If "developing" means changing the actual look or dimensions of the long piece:
: Look for the subroutine that generates a random number between 0 and 6.
Modifying or "developing" a specific piece like the "long piece" (I-piece) in a Tetris ROM for MAME generally requires or using cheat codes , as the game's logic is hardcoded into the original binary.
: The rotation logic is stored in data tables within the ROM. Modifying these requires identifying the table offsets to change how the piece behaves when you press the rotate button. Identification Table (Sega Tetris Example) Common Memory Location Long Piece (I) 01 Often found near the "Current Piece" variable Square (O) 02 Used for piece-type identification in code