NanamiWatabe

Many Japanese MMD model creators are open to edit their models.
Still this never means you can do whatever you want to the models.
I have to say most modelers are negative to frankenstein models.
Editing means you yourself make new clothes, hair, or other parts from scratch for the models you want to edit.
Swapping heads or other parts is not editing. It is rather called frankensteining.
Think about this example. You collect many famous pictures. Michelangelo, Gogh, Millet, Picasso and other artists.
You cut their works and make a new patchwork picture.
Is this an art? Can you claim you edited the picture?
Or it can be compared to cutting dolls into parts to create a "new doll of your own".
Can you say you treat the dolls with love?
Definitely not! You just destroy original pictures or dolls.
Making frankenstein models is like this. You just destroy original models.
Modelers were tolerant to editing because they had the slightest idea that people would make frankensteins. They hoped pe

Well, you can edit and distribute editable MMD models, but modelers usually set additional conditions for editing and/or redistributing (and of course, trading) their models.
DO NOT EDIT AND/OR REDISTRIBUTE (and trade) MODELS UNLESS YOU HAVE THE FULL COMMAND OF JAPANESE TO READ THE ATTACHED TOS.
Full command means you can read Japanese newspapers or academic papers. Basic conversation skill is not enough. You should also refrain from distributing your translation unless you have the full command of Japanese. If you spread a grave mistranslation, you would be involved in a copyright trouble.
In addition machine translators are not reliable. Japanese language has tons of homophones, conjugations and particles. A slightest misreading leads to the total nullifying a sentence.
Here is an example.
"Be not afraid of greatness: some are born great, some achieve greatness, and some have greatness thrust upon them."
↓ Googled
"偉大さを恐れて

Japanese people have the special affection for human-shaped objects.
With the influence of Shinto culture, they often regard human-shaped objects as resting or residing room for souls, spirits or gods/deities. Though this custom is becoming obsolete, some Japanese take old dolls to shrines or temples to pray for the repose of souls. Priests or monks recite a sutra and the dolls are cremated. These might be the reason why some people in Japan often talk as if Vocaloid characters were real human beings.
It seems some MMD model creators take their works as the very expression of their souls with this cultural and religious belief. This strong affection for human-shaped objects may lead to the reason why they strongly reject editing or redistributing their models. They don't mean to be selfish at all; we should respect their feelings.