$string = "useridagohiluserid>traderidagohiltraderidjiagohilji";
if ($string =~ /traderid(.*?)traderid/sig)
{
   $string =~ s/$1/myword/ ;
}
print "$string\n" ;

##</code><code>##

useridagohiluserid>traderidmywordtraderidjiagohilji

##</code><code>##

useridmyworduserid>traderidagohiltraderidjiagohilji