How about appending the asterisk to the variable before it's printed:

format LEVELS=
USGS @<<<<<<<<<<<<<< R=234* T=A* 235#@<<<<<<<* 709#@<<<* 234=L* 
$file2{$grid}, $date, $time, $level
USGS @<<<<<<<<<<<<<< 239=@*  
$file2{$grid}, $method.'*'
.
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I'd like to be able to assign to an luser