jQuery.extend(jQuery.jgrid.edit, {/* new default values */});
Default values of any parameters of editGridRow including all you listed can you change in the way.
If use use a parameter of editGridRow directly in the call of the function editGridRow or indirect as parameter of navGrid then will be used the parameters and not default values. So all is very easy.
I use for examples in all jqGrids which I use in inline or form editing recreateForm: true. So I included ovewriting default parameters in one JavaScript file which I load in all my pages (in my master page). It maks the code which I write for every grid shorter.
I see no performance problems with the usage of default parameters.
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