I've done this successfully, following this down and dirty mini tutorial someone wrote out for me:
Load the skintone with simpe,
be on plugin view,
use the window at the top left - go to texture image and select the age and gender image you want to add on to.
When the image loads you will have an option to export - do this and save in your pic's folder.
Load and do the same for your fiddley bits file.
Load the exported image onto an editing program,(i use GIMP 2.0 myself) alter the image (copy parts and paste) and use SimPE to import,
commit and save.
I hope this makes sense to you...if you have any questions, I might be able to answer them, but I am mostly simpe illiterate. But I figure if I could do it...you probably can, too. Good luck!!