Hello stan,
to make the head models you'd need PeoplePutty which you can purchase from Haptek. Or you can simple texture the Heads that are already out.
to make full bodies requires alot more, for that you'll need other Haptek tools, which I was quoted around $2,400.00 to purchase.
to make accessories as I do you'll need 3DS Max, a graphics program like Paint Shop Pro, and the Haptek Acessory Converter tools, the Haptek tools run $100.00.
The way most people do it are using PeoplePutty and just making new heads, or using graphics programs and re-doing the textures and changing the looks of the heads and full bodies. The easiest of all of course is just edit the textures, or shall I say the cheapest, anyways, I hope this information helps.