Start off by clicking "edit", then "find."  Type in the text string lnz for the baby you want to hex based on the code you're using:
 
ab.lnz Asian Boy:  short hair, bald/dots, curly, sparse.  
abx.lnz Asian Boy:  full hair, 1 curl, 1 strand, mohawk.
ag.lnz Asian Girl:  two Ponies, bald/dots.
agx.lnz Asian Girl:  one and three ponies, mohawk, 1 curl.
bb.lnz Black Boy:  short hair, bald/dots, curly, sparse.
bbx.lnz Black Boy:  full hair, 1 curl, 1 strand, mohawk.  
bgx.lnz Black Girl:  one and three ponies, mohawk, 1 curl.
bg.lnz Black Girl:  two Ponies, bald/dots.
brb.lnz Tan Boy:  short hair, bald/dots, curly, sparse.
brbx.lnz Tan Boy:  full hair, 1 curl, 1 strand, mohawk.
brg.lnz Tan Girl:  two Ponies, bald/dots.
brgx.lnz Tan Girl:  one and three ponies, mohawk, 1 curl.
wb.lnz White Boy:  short hair, bald/dots, curly, sparse.
wbx.lnz White Boy:  full hair, 1 curl, 1 strand, mohawk.
wg.lnz White Girl:  two Ponies, bald/dots.
wgx.lnz White Girl:  one and three ponies, mohawk, 1 curl.
To change the babyz hair color, you'll need to know what color hair the baby will already have based on it's code, or atleast an idea.  Scroll down quite far in your babyz lnz section, until you come to the section that shows the bitmaps used to color the babyz hair.
This is a section for a white boy (wb.lnz) Each babyz hair color has its own file.  The files are as follows:
 
B_Afro1
B_Afro2
B_Afro3
B_Blond1
B_BbrownLong1
B_DarkBrown1
B_DarkBrown2
B_DarkBrown3
B_DarkBrown1_Trans
B_DarkBrown2_Trans
B_DarkBrown3_Ttrans
B_LtBrown1
B_Orange1
B_Orange2
B_Trans1
B_Trans2
B_Trans3
B_TransNew1
B_TransNew2
B_TransNew3
B_TransNew4
Below Simon, a full haired white boy,  will model all of the different options of hair color.
Simply find the hair color of your code baby, and change it to any one of these options available in the babyz game!  Say you are changing a dark brown haired boy's hair to B_TransNew3.  You will only change the bmp file, because the source is the same in the babyz game, see the example below.
If you want to hex a whole new hair file, then go here for more info!  If not, scroll on down to learn how to add more hair, or tweak the eye brows!
Want your full haired boy to have a big more hair?  Maybe longer bangs?  All the info you need for hexing can be found right in the babyrez.dll  As you can see on the left, the paintballz section is explained.  This section is where you can make the base of the boy's (or girl's) hair become bigger.  The main thing you need to know is where to find the diameter, which controls the area of the head that is to be covered.  This part will allow you to make the base hair cover a larger portion of the head.  This is all I will be showing you, but you can experiment with the other stuff.
Above, the diameters have all been changed to 80.
 
 
The Baby on the left is a normal full haired baby.  The baby on the right is the result of making the diameters all 80.
Most of the brows for boys end up just being the same as the hair color.  Girls brows, however, are always the same thing!  They can't be thicker either!  But they can now that you know where to find the info.  Let's use a white girl for this example.  So after you type in Wg.lnz to get to the girl, scroll way down past the eye color info and hair files.  You will come to a section that's called [Ballz Info]
Here is the eyebrow section.  After finding the [Ballz Info] section, keep scrolling until you see this part where it mentions eyebrows.  The numbers in red are the ones to change the brow color.  The ones is blue change the thickness.  0 is the normal thin brows.  Change it to a 1 to make thick eyebrows like the baby below.
Of course you can pick ANY color from the babyz chart that you wish.  Be careful not to change other numbers, and remember that if you're using a 3 digit number, overwrite the first "." and not the "," behind the original number.  Have fun hexing!