well the method I mentioned fell apart when trying to pass $1, $2 etc to be interpolated as captures, so you and ikegami are right, it really needs an eval. I did want to stick with the script 'pattern' 'replacement' format however (rather than script 's/pattern/replacement/') so I used this instead:

#!/usr/bin/perl -wl
use strict;

my ($arg_1, $arg_2) = @ARGV;

$_ = "apples";

my $expr = "s/".$arg_1."/".$arg_2."/";
eval $expr;
print;

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./test.pl '\x61(.*)\x73' '\x41$1\x53'
AppleS
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