Big endian or Little endian?

I was making a chart to log the password patterns in Megaman X for different items and events as follows:

Beating Storm Eagle modifies the PW like this:
_= didn't change
*= changed

___*
*_*_
__*_

So if I were to put that in binary it would be:

0001
1010
0010

The thing is, it's 1 byte and 1 nybble. There's two ways I could organize this (red means padded 0s):

Taking the first 8 as they come and pad
00011010 00000010 (1A 02 in hex)

Taking the first 4 bits and treating it as a nybble:
00000001 10100010 (01 A2 in hex)

I'm curious, is this how big endian and little endian are? Or is it simply Flipping the 4 bits in a byte to change something like FA to AF? It's not something that's preventing me from completing my project. And this isn't just concerning a Megaman game either. But I'm certain this question would be asked sooner or later by someone who just learned hex and got lost in a 68k tutorial.

*For those just learning hex, a nybble is a 4-bit binary number such as 1011 (a single hex digit or half-byte).

 

Does that mean a word containing bits 1234 would be 4321? Maybe I misread. But according to HiveBrain's Sonic 2 SMS Guide, the 2 bytes in a word were reversed, and no changes were made to the bits in any way. So that would mean:

byte ab would remain as ab
word 00ab would become word ab00

Does that mean a longword 000000ab would be 0000ab00? Or does the 2 words in a longword get swapped as well, making it ab000000?