I had made a collection of bits that were created and given an indexed material value that I wanted to control parametrically, basically as per the post from Wrathchild the entire ind(material...) chains could be replaced by the parameter name - the point I missed when first trying this was the need to get all of them for each element.
Before
sprism_{2} "Paint-01","Paint-01","Paint-01",
57, 0, 0, 1, 0, -1.495322479477, 0,
0, 0, 1, 0, 0, 0,
-0.6325, 1.103805482683E-16, 79, ind(material,"Paint-01"),
-0.6285229727575, -0.07081753113534, 79, ind(material,"Paint-01"),
-0.616641904455, -0.1407444907274, 79, ind(material,"Paint-01"),
-0.59700620642, -0.2089015066866, 79, ind(material,"Paint-01"),
-0.5698628089483, -0.2744314649919, 79, ind(material,"Paint-01"),
After
sprism_{2} AC_SPK_MAT, AC_SPK_MAT, AC_SPK_MAT,
57, 0, 0, 1, 0, -1.495322479477, 0,
0, 0, 1, 0, 0, 0,
-0.6325, 1.103805482683E-16, 79, AC_SPK_MAT,
-0.6285229727575, -0.07081753113534, 79, AC_SPK_MAT,
-0.616641904455, -0.1407444907274, 79, AC_SPK_MAT,
-0.59700620642, -0.2089015066866, 79, AC_SPK_MAT,
-0.5698628089483, -0.2744314649919, 79, AC_SPK_MAT,
Probably really obvious now DOH!