//select your text, then execute the macro
if (document.selection.IsEmpty){alert('Nothing selected?'); quit();}
SelText = document.selection.text;
alert(SelText); // <== only for testing


//Settings:
MatchREx = "(.+?\t).+\t(NOT SENT|SENT)"; //Match/Find this
ReplWith = "$1$2"; 			//Replace with that
REModify = "gi"; 	//(G)lobal, (i)gnor case, (M)ultiline


//How many matches?
Matches = SelText.match(RegExp(MatchREx,REModify)).length;

//Do the RegEx search&replace itself:
ReplacedStr = SelText.replace(RegExp(MatchREx,REModify),ReplWith);


//The output:
alert(Matches + ' matches found'); // <== only for testing
alert(ReplacedStr); // <== only for testing

//Overwrite the selected text:
//document.selection.text = ReplacedStr;