Our pickups don't have covers like some other brands. The decorative part of the pickup is either 1) a plastic or wooden shell filled with polyurethane or 2) molded polyurethane or molded polyurethane with a wood veneer face. In any case there is not a removable cover, and the whole pickup would need to be replaced.
That being said, you can order pickups with any decoration you like after the fact, but it's not advisable with Series I/II since the pickups need to be matched to the circuit. You'd have to send your bass in and get it upgraded at the same time.
For AXY or MXY pickups, you can order them, and the price would be quoted per job. It depends on the wood and the workload and how fast you want them.
You can order wood backplates after the fact too, but they can only retrofit from plastic, since the brass plates are much thinner than the wooden ones. Of course, they can't be continuous. We usually coordinate with the top wood, since most plastic backplates are on instruments without a back laminate. In your case, j_gary, the cover would sit proud of the back of the bass and not look so good.
