Update the data before viewing the tables

Hi,
I would need to update a negative value. For example my data is -10, i delete the "-", i color the line in red and the displayed data must be 10.
So i should update the json which returns me the php.

This is my code:

"rowCallback": function( row, data ) {
if ((data.imp < 0 && data.iuv != '') || data.st == 'D') {
$('td', row).css( 'background-color', '#ff6347' );
var val = data.imp.substr(1);
console.log(val);
}else if ((data.imp > 0 && data.iuv != '') || data.st == 'M'){
$('td', row).css( 'background-color', '#FBB917' );
}else if ((data.imp > 0 && data.iuv == '') || data.st == 'N'){
$('td', row).css( 'background-color', '#3cb371' );
}
},

How can i do?

I have read online .... but i have not found anything that was useful for me!

Thanks