Modding Help Context-sensitive textures

Hi, is there any way to change certain texture if requirements are met? Like change arms textrure if player wear certain chestwear or change body texture if he wears no chestwear.

I think it should look like this:
"Function ?()
if player.getItemSlot(legs) == "none" and player.getItemSlot(legsCosmetic) == "none"
then
?
else
?
end
end"
But I don't know how to change a texture using lua.