Look at HTMLLink.
Thanks for the hint. Unfortunately, the "[id]" String is generated in UISelection.java, a core file of Seam. I thought I could do that change by just building a new annotation, but now I see it isn't possible without changing Seam itself. And I refrain from doing that.
Well, so I think I'll just forget the multple editor window stuff or the DataModel annotation due to the problems. It's a pity ;).