Here is a full hack which changes all the level layouts for Super Mario Bros. Also some of the enemies more faster and also the mushrooms trail away quicker from their source blocks to add difficulty.
Super Mario Bros. (World).nes - NOINTRO
CRC32: 3337EC46
MD5: 811B027EAF99C2DEF7B933C5208636DE
SHA-1: EA343F4E445A9050D4B4FBAC2C77D0693B1D0922
SHA-256: F61548FDF1670CFFEFCC4F0B7BDCDD9EABA0C226E3B74F8666071496988248DE