Does \definemathcommand [xyz] [nolop] {xyz} do what you want?
Not really if, instead of xyz, I want a name with hyphens, quotes, stars or colons. Compare the output of \definemathcommand[xyz][nolop]{fancy-function-name'*.:} in ConTeXt with the output of \DeclareMathOperator{\xyz}{fancy-function-name'*.:} in LaTeX. What I can do is \definemathcommand[xyz][nolop]{\kern\zeropoint\mfunction{fancy-function-name'*.:}} which gives the same result as \DeclareMathOperator, except for the hyphens and the star are converted into binary operators and the colon which is preceded by a space, since I didn't use \newmcodes@, that is why I asked how to implement the macro \newmcodes@ in ConTeXt, which is defined in LaTeX as \begingroup \catcode`\"=12 \gdef\newmcodes@{\mathcode`\'39\mathcode`\*42\mathcode`\."613A% \ifnum\mathcode`\-=45 \else \mathchardef\std at minus\mathcode`\-\relax \fi \mathcode`\-45\mathcode`\/47\mathcode`\:"603A\relax} \endgroup so that the following code can compile in ConTeXt: \definemathcommand[xyz][nolop]{\newmcodes@ \kern\zeropoint\mfunction{fancy-function-name'*.:}} Maggyero