I tried to change the art for the HUD in Sonic 2 just now. Simple extract, decompress, edit in TLP, recompress, reinsert job. When I readded it I found that the data was eighteen bytes shorter than the original. Fine, no problem, fill the rest with null bytes until the correct end of the art. The result was as in the attached screenshot: the E in SCORE is still in italics, even though the rest of the HUD is not.