keep the hexnumbers as strings ...

  DB<121> $SM = 0xFE;
 => 254
 
  DB<122> $SM = "0xFE";
 => "0xFE"
 
  DB<123> print $SM
 => 1
0xFE
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...or write a subroutine printhex() which automatically fulfills your wishes by converting any numeric scalar to a hexstring before printing.