my $AoH_new = map ...

##</code><code>##

my $AoH_new = map { $AoH_orig->[$_]{'title'} =~ s/ /_/g } @$AoH_orig;

##</code><code>##

my $AoH_new = map { $_->{'title'} =~ s/ /_/g } @$AoH_orig; 

##</code><code>##

my @AoH_new = map {       ## store the result in an array
    my %h = %$_;          ## make a copy of each hashref
    $h{title} =~ s/ /_/g; ## modify a value in the hash copy
    \%h;                  ## return a ref to that copy
} @$AoH_orig;

##</code><code>##

use Storable 'dclone';
my $AoH_new = dclone $AoH_old; ## copy the old structure

## change an item in each hash in the new copy
$_->{title} =~ s/ /_/g for @$AoH_new;