Seemed like a good spot for look behind and lookahead :-)

my $test = 'Patron @FirstName@ @LastName@ has filled out the @FormName
+@ form. Please send them an email at 

@EmailAddress@.';

$test =~ s/(?<=@)        # starts with @ (but don't grab @)
       ([a-zA-Z]*)        # string of letters
           (?=@)        # ends with @ (but don't grab @)
      /<b>$1<\/b>/xg;    # put $1 back with bold tags around it. @ are
+ preserved.

print $test;
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___________
Eric Hodges