You said that you wanted \LuigisWhateverShouldHappen macro to be executed, which in turn means that \immediate\write18 is executed, the text Something .... reason is written to the pdf, and the macro \imediate\write18 is executed.
If you do not want the text to be written to the pdf, do not add it to \LuigisWhat... macro :-) true, but not so robust.
\def\LuigisWhateverShouldHappen{..what ever...} \appendtoks\LuigisWhateverShouldHappen \to \everylastshipout \starttext hello \stoptext I want be sure that "..what ever.." will never introduce differences with \startext my stuffs here \stoptext for *ever* "my stuff here" and for *ever* "..what ever.." I believe that it's no possible. Anyway \def\LuigisWhateverShouldHappen{..what ever...} \appendtoks\LuigisWhateverShouldHappen \to \everylastshipout \starttext hello \stoptext can be good enought . -- luigi