I have added detail to many of them by taking another bump map and editing it.

You can add a lot of detail to any character by doing this. 

There are ways of doing complete procedural details, but it is rather complex and requires a huge network of nodes to do so accurately.

As an example, you can use two wave2D nodes as the basis to add or replace detail to just the nipples on a character. 

This is a nipple bump example on V3 with 8k textures. It modifies the original bump used, but only shows part of the shader..

The entire character can be done like this, but it is a lot of work.

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