Hi!
U can do it using script
Look the demo report "change_item_from_script.lrxml" from demo_r1\demo_reports
It's can help you.
Below sample from that demo report
$S{
var color = new QColor('#DEB887');
var font = new QFont('Times New Roman',26,false,true);
THIS.backgroundColor = color;
THIS.fontColor = QColor('red');
THIS.font = font;
'Test'}