A common way to address the individual bytes of a word (or larger)
variable is to split it as an array of bytes.

This can be done as follows

var word w
var byte wb[2] at w

You can then refer the two bytes of the word w as wb[0] and wb[1]

To define bits within a byte, you may do the following:
var byte my_byte
var bit my_bit at my_byte : 0
var bit*3 my_bits at my_byte : 1

If the individual bytes of an array need a specific name alias keyword can be used as given below.

This website has a very good introduction PICs and JAL available at http://justanotherlanguage.org/content/jallib/tutorials/tutorial_getting_started
The original author, Wouter too has a Starting With PIC guide which is a bit dated.

JAL is TLA (Three Letter Acronym) which stands for Just Another Language