On 2013–10–08 Procházka Lukáš Ing. - Pontex s. r. o. wrote:

> I'm trying to hook commands.stoptext()...

There is already a hook for that. No need to tinker with Lua.

\setupexternalfigures
  [location=default]

\setupdocument
  [after=\setups{document:after}]

\startsetups [document:after]
  \startTEXpage
    \externalfigure [cow]
  \stopTEXpage
\stopsetups

\startdocument
  \input knuth
\stopdocument

Marco