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

so that the following code can compile in ConTeXt:

\definemathcommand[xyz][nolop]{\newmcodes@\kern\zeropoint\mfunction{fancy-function-name'*.:}}

Maggyero