G'day Bill,

Welcome to the Monastery.

You're almost there. Just change the '.' in your regex to '[^(]'. Here's your code with that change (plus a small modification to the shebang line for my purposes):

#!/usr/bin/env perl
use strict;
use warnings;

my $x = '((A & B)\' | (A & C & (A & B & D)\'))'; 

print "Given: $x\n"; 

#$x =~ s/(\(.*?\))\'/\!$1/g; 
$x =~ s/(\([^(]*?\))\'/\!$1/g;

print "Calculated: ",$x,"\n";
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Output:

Given: ((A & B)' | (A & C & (A & B & D)'))
Calculated: (!(A & B) | (A & C & !(A & B & D)))
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