01. Simply put - Thank you haukex and Marshall.

02. Yes, adding a 'sleep()' Command below each '$port->write*()' solved my Dilemma. However, I used 'Time::HiRes' - usec() Function for delays less than 1 Second.

I also see the usefulness of the ''IO::Termios' Module' Functions.

Below is a complete Code Example:

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

use Device::SerialPort;
use Time::HiRes qw(usleep);

sub Handle_FTdx1200{
 my $delayValue=100000;
 
 my $port = Device::SerialPort->new("/dev/cu.usbserial");
 $port->databits(8);
 $port->baudrate(4800);
 $port->handshake("rts");
 $port->parity("none");
 $port->stopbits(1);
 $port->write_settings || undef $port;
 
 $port->write("FA;");
 usleep($delayValue);
 my $VFOA=$port->read(11);
 
 $port->write("MD0;");
 usleep($delayValue);
 my $Mode=$port->read(5);
 
 $port->write("PC;");
 usleep($delayValue);
 my $Pwr=$port->read(6);
 
 $port->close();
 
 $VFOA=substr($VFOA, 2, 8);
 $Mode=substr($Mode, 3, 1);
 
 $Pwr=substr($Pwr, 2, 3);
 $Pwr=int($Pwr);
 $Pwr="$Pwr";
 
 return($VFOA, $Mode, $Pwr);
}

my ($tFreq, $tMode, $tPower)=Handle_FTdx1200();

print($tFreq);
print("\n");

print($tMode);
print("\n");

print($tPower);
print("\n");
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03. Apparently, in my initial Perl Code, I did not try the 'sleep()' Function.
It is in AppleScript that a delay Function, after any 'serialport Function, is required.

Below is AppleScript Code to set the Keyer Speed to 38 Words per Minute.

set desiredPort to "/dev/cu.usbserial"

set tSpeed to "38"

try
    set tPort to serialport open desiredPort bps rate 4800 data bits 8
+ parity 0 stop bits 1 handshake 3
    delay 0.1
    
    serialport write ("KS;") to tPort
    delay 0.1
    
    set originalSpeed to serialport read tPort
    delay 0.1
    set originalSpeed to (get (characters 4 through 5 of originalSpeed
+) as string) as integer
    
    serialport write ("KS0" & tSpeed & ";") to tPort
    delay 0.1
    
    serialport write ("KS;") to tPort
    delay 0.1
    
    set currentSpeed to serialport read tPort
    delay 0.1
    set currentSpeed to (get (characters 4 through 5 of currentSpeed) 
+as string) as integer
    
    display dialog "Original Speed: " & originalSpeed & return & "Curr
+ent Speed: " & currentSpeed giving up after 5 buttons ("OK") default 
+button "OK"
    
    serialport close tPort
on error
    serialport close tPort
end try
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In conclusion - again, thank you - to the both of you.