Can I edit BlockPlaceholder in dynamic blocks?

[Lindsay]

I have a dynamic block that I am using BlockPlaceholder to display attributes. Its ended up being a fairly complicated set of instructions to get the information I want to display. My problem is that I can't figure out how to edit a placeholder once I have created it. As I continue to refine how it works, I'm having to recreate the placeholder from scratch each time I change a parameter.

Anybody have an idea of how to do this? I keep thinking its something quite simple that I have missed but i haven't found it yet...

Thanks.