Consider to use get/set of the data parameter of the jqGrid. It holds all the data of the local grid. The corresponding code can be about following

var mydata = $('#list').jqGrid('getGridParam','data');

After modification of the grid data with respect of $('#list').jqGrid('setGridParam','data',mydata) refreshing of the internal grid's indexes with the code $(“#list”)[0].refreshIndex() can be needed (see this for more detailes).

Best regards
Oleg