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 cut
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 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