Ext.override(Ext.grid.ColumnModel, {
    addColumn: function(column, colIndex) {
        if (typeof column == 'string') {
            column = { header: column, dataIndex: column };
        }
        var config = this.config;
        this.config = [];
        if (typeof colIndex == 'number') {
            config.splice(colIndex, 0, column);
            //handling the id of config to fulfill the drag&drop (when enableColumnMove is true) problem
            for (var i = colIndex + 1; i < config.length; i++)
            {
                var id = config[i].id;
                if (typeof id == 'number') {
                    config[i].id++;
                }
            }
        } else {
            colIndex = config.push(column);
        }
        this.setConfig(config);
        return colIndex;
    },
    removeColumn: function(colIndex) {
        var config = this.config;
        this.config = [config[colIndex]];
        config.splice(colIndex, 1);
        //handling the id of config to fulfill the drag&drop (when enableColumnMove is true) problem        
        for (var i = colIndex + 1; i < config.length; i++)
        {
            var id = config[i].id;
            if (typeof id == 'number') {
                config[i].id--;
            }
        }
        this.setConfig(config);
    }
});