If you want to make your character taller or shorter than MP character creator allows you:
1. Create your character in SP and set the character height tallest/shortest possible
2. Press CTRL+C in character creation screen in SP (it should copy a code that you can save if you want)
3. Launch MP and MP character creator
4. Press CTRL+V twice and and now your character should be taller or shorter than MP limit
5. Press Done
If you open the character creation window in MP in the future, you have to paste the code again, otherwise your character height will reset to MP default limit.
Not sure how you actually edit character build in MP, but I haven't tested too much, because this is a exploit.