No idea about the item IDs.
I think I noticed that characters created with the same name tend to have the same last few digits, but not entirely sure.
Here's the proportion stuff.
Explanation of why this works:
The game uses the same base female and male model for several characters.
It just adjusts their default size and proportions. These happen to be saved into the database.
So, by editing the database, we can reshape the characters into other characters' proportions.
We can also ignore the in-game slider limits.
List of proportion-related database values:
The changes will update when you enter/exit the character select screen, and maybe the Avatar Shop.
You won't see some changes in Avatar Shop unless you go to the Dye Shop first, and then go back.
In the "Costume" table. Type, Key, CostumeSN (replace x with new values):
0, 3, x (default hairstyle, corresponds to player_costume.txt hair values)
1, 0, x (default eyebrows), c1 (eyebrow color)
0, 1, x (default innerwear, corresponds to player_costume.txt innerwear values)
0, 2, null, c1 (skin main), c2 (skin shadow), c3 (eye color)
2, 1, x (height, usually around 70-106, there's an in-game limit despite char select looking tiny/huge)
2, 2, x (breast size, 70 to 120 is normal, high values look blocky, elongated, clipping through clothes)
3, 15, x (more muscle, normal values are 0-1000)
3, 16, x (thinner body, normal values are 0-1000)
3, 17, x (fatter body, normal values are 0-1000)
3, 18, x (thinner waist, normal values are 0-1000)
3, 19, x (fatter waist, normal values are 0-1000
3, 20, x (thinner arms, normal values are 0-1000)
3, 22, x (thinner legs, normal values are 0-1000)
3, 23, x (fatter legs, normal values are 0-1000)
3, 24, x (thinner shoulders, normal values are 0-1000)
3, 25, x (wider shoulders, normal values are 0-1000)
3, 40, x (fatter arms, normal values are 0-1000)
Note that you can go over 1000. I haven't done much testing with negative values.
Character shape: (you can add several of these to influence character overall shape)
3, 101, 1000 (Kai's body shape: wider shoulders, etc)
3, 102, 1000 (Vella's body shape: thinner calves, wider hips, etc)
3, 103, 1000 (Lynn's body shape: wider calves, less curves, etc)
3, 104, 1000 (Arisha's body shape: larger breasts, thinner waist, thinner calves, etc)
As far as I know, there isn't a way to only make the hips wider without affecting other stuff.
Unknown (either no noticeable difference or I haven't tested yet):
2, 3, 0
2, 4, 0
2, 5, 0
2, 6, 0
2, 8, 10
2, 9, 10
2, 10, 10
2, 12, 3
2, 13, 3
2, 14, 1
3, 31, 0
3, 36, 0
3, 37, 0
3, 41, 0
There may be other values for males, but I haven't experimented with male characters much.
Example 1, giving Lynn a more womanly/curvy body:
She already has 3, 103, 1000 by default. That defines her Lynn body shape.
Change that to 3, 103, 0. That should revert to Fiona's body shape.
You can also remove 3, 103 or simply change it to 3, 102 or 3, 104.
Then I 'd add a new row for either 3, 102, 1400 or 3, 104, 1000, or a mix of those.
Those should make her chest larger, waist thinner, hips wider, calves thinner.
Then I'd change 3, 23 to 400 (3, 23, 400). That would make the legs fatter.
Combined with 3, 102 and 3, 104 the legs should now look more womanly.
2, 2, 100 to make the chest more prominent.
Example 2, making Arisha look younger (ie. Lynn's body):
She already has 3, 104, 1000 by default. That defines her Arisha body shape.
You can remove 3, 104 or simply change it to 3, 103.
If you didn't change 3, 104 to 3, 103, add a new row for 3, 103, 1000.
Change 2, 2 to a low value, around 55 (Lynn's default chest size).
Change 2,1 to around 89 (Lynn's default height).
Screenshots: