$txt_original="Arkarmit ithaaatokkk ide? aaaztamindenit. tokkkal-vonoval";
$txt_replaced=$txt_original;

# megkeressuk a szukseges mintat
$txt_replaced =~ s/aaa(\w{5})/aaa12345/g;
# Ami a $1-be kerul. Onnan atmentjuk $text_to_replace -be
$text_to_replace=$1;

$txt_replaced =~ s/$text_to_replace/12345/g;

print("Original: ${txt_original}\n");
print("Replaced: ${txt_replaced}\n");

# output:
# Original: Arkarmit ithaaatokkk ide? aaaztamindenit. tokkkal-vonoval
# Replaced: Arkarmit ithaaa12345 ide? aaa12345ndenit. tokkkal-vonoval