[NTG-context] \setuphead and \startchapter request

I would like to use, for example, \setuphead [chapter] [after={\placecontent\blank}] But sometimes, I would like to use something like \startchapter [number=no,incrementnumber=no,after=, title={Conclusions of the first part}] \stopchapter 1. I request to have after=, (and other setup head keywords) taken into account, or some other mechanism, so as here not to \placecontent for a specific instance of \startchapter. 2. If I have: \setuplabeltext [chapter=Chapter ] % with trailing space; blank by default would there be some way to specify chapter=, (or another mechanism) to have the Chapter label blank for a specific instance of \startchapter? Thanks Alan