$rplc = "\\x41";
print $rplc;    # prints the string \x41

$_ = "apples";
s@a@$rplc@;     # variable containing the string \x41 used in RHS
print;          #   - not interpolated to the char A

$_ = "apples";
s@a@\x41@;      # \x41 hardcoded into RHS
print $_;       #   - interpolated to the char A

__END__

outputs:

\x41
\x41pples
Apples