I created this custom by taking an ARC Trooper and removing the head and simply adding a bald head, mine was from a Mace Windu miniature that was used in a conversion to create Jedi General Di.
Here is the unpainted conversion.
Before I cut off the original head and glued the new head into place I gave it a basic paint job to resemble this picture from the Clone Wars series in hopes that it would look OK before I ruined a perfectly good model.
The helmet will be saved, repainted and placed on the base next to his feet as if he dropped it. I found a decent photo of someone’s custom clone helmets and used this for inspiration and I followed this picture of his armor to try to emulate the look needed.
And here is the final piece.