“Hex Tweaks” are loosely defined as sets of single-or-multiple-byte-changes that can be preformed for desirable effects. There is no clearly-defined upper limit for the number of bytes that can constitute a 'hex tweak' but they are usually less than 16 bytes' worth of changes.

Tweaks for the mechanics of Samus.

0x96C - 40 to 58
0x980 - 3F to 57
0x9F3 - 70 to 58
0xA07 - 71 to 59
Centers Samus' horizontal position during movement where the screen scrolls horizontally.

0x1C2A - 01 to 02
0x1C6D - 01 to 02
Samus runs faster on the ground.

0x1C99 - 02 to 03
0x1CCA - 02 to 03
Morph ball rolls faster on the ground.

0x1CFB - 01 to 02
0x1D27 - 01 to 02
Samus moves faster in air.

0x11C3 - $32 to $98
0x11C4 - $11 to $1C
Spider Throw works both ways

0x1899-0x18E6 - Fill with non-zero values (doesn't matter what)
Space jump timing is free.

0x573D: C0 to C9
Respawning blocks don't hurt Samus, and they don't destroy themselves after spawning on her.

0x57D7: 02 to ??
Adjusts damage that respawning blocks do to Samus.

Tweaks for beams, missiles, and bombs.

0x51A1 - Everything up to 0x51C1 becomes 04
Makes missiles fire at a faster and more consistent speed.

0x53FC - 60 to ??
Changes the amount of time it takes for a bomb to explode. Change this to 30 for Super Metroid's bomb explode time, or 20 for Zero Mission's.

0x50D5: 83 to 94
Makes the Wave Beam use an alternate movement table (looks like a discount Spazer when motion blur is on).

0x50DD - 7E to AF
Wave Beam doesn't wave anymore :(

0x509E: D0 to 00
0x50BB: D0 to 00
Spazer splits indefinitely, effectively turning it into a spread gun

0x50AC: 02 to ??
0x50B3: 02 to ??
0x50C9: 02 to ??
0x50D0: 02 to ??
Adjusts the speed that the Spazer splits apart.

0x509D: 05 to ??
0x50BA: 05 to ??
Adjusts the length of time that the Spazer splits apart (more time makes it wider).

0xEDDA: 96 to ??
Adjust the Metroid Queen's initial health.

0x2C83: C8 to 00
Pausing now works during the Metroid Queen fight.
NOTE: This tweak creates two minor graphical issues:

1. Certain animations will continue playing while paused (e.g. the feet stomping)
2. The flashing palette effect will not apply to the portion of the screen below the queen.

Other than that, it appears to be perfectly usable.

Tweaks for anything collectable–items, expansions, drops.

0x374D - 01 to 05
0x3752 - 01 to 00
Makes items and E-Tanks play the shorter, quicker acquisition jingle, just like Missile Tanks.

0x8267 - 20 to ??
Changes the amount of energy a large energy drop will add.

0x8270 - 05 to ??
Changes the amount of energy a normal energy drop will add.

0x82AC - 05 to ??
Changes the amount of missiles a normal missile drop will add.

Tweaks that don't quite fit in with any of the particular categories.

0x190E - 56 to FF
Makes a spin jump fly upward forever if you release A before the apex of the jump. Hitting a ceiling or shooting will cancel it. Best combined with Respin.

0x2CB6 - 28 to 20
0x2D02 - 20 to 28
Enables debug menu on pause.
Note: This reverses how RAM address D0A0 reads flags 00 and 01.

0x2CE4 - 01 to 02
Music keeps playing on pause.

0x58C5 - CB 37 3C to 3E 00 00
Disables low health beep entirely.

0xAA2E - C0 to 00
Makes hatches vulnerable to beam fire.

0xAA43 - 05 to ??
Changes the amount of missiles it takes to open a hatch.