I have given some Chaos Space Marines new helmets, gathered from some Chaos Knights. The Lamenters are now done. They were a challenge. The original paint job by Jamie (the previous owner) was great, especially the chequy. I would have left them untouched if it weren't for a suggestion from Lewis to give them Jet Packs. An Ebay purchase supplied them with some old metal packs, already painted yellow. A different yellow to the marines power armour. Some subtle washes with Army Painter soft tone and highlighting with Flash Git yellow helped make the upgrade look more natural.
I changed some poses, added a skull here and an arm there, as well as repainting minor details on the armour. Plastic miniatures are easy to convert. However, with the new metal Jet Packs making the space marines top-heavy, washers were required to help balance them. One of them needed lead 'rocks'.
God be with you and have a blessed week.