It is not clear what you mean by "building up another character generation system".

Even if you bought the characters, modifying them with the intent to resell them is governed by the Reallusion EULA as well as the DAZ EULA if the character was DAZ originally. Using in games is OK, but if you want to sell the games you will need permission. Using in rendered videos has no restrictions.

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I can't use the characters or their morph assets to build up another character generation system in games or interactive services???
If I just want to use CC3's skin and clothing automatic weighting function, the characters and clothing models are made or bought by myself, such as DAZ and so on. Are users subject to this restriction?