"Type" old and new passwords into Windows Server 2016 change password screen when WorkSpaces doesn't allow pasting from your Mac.

change_pass.applescript

#!/usr/bin/osascript

# Usage:
# export OLDPASS="oldpasswordhere!"
# export NEWPASS="newpasswordgoeshere."
# get to change password screen in WorkSpace prior to running this script and make sure you're on the "old password" field.
# run script without args

on sysKeyCode(kc)
	tell application "System Events" to key code {kc} using {command down}
end sysKeyCode

on sysKeyStroke(ks)
	tell application "System Events" to keystroke ks
end

on sendString(thePass) 
	set AppleScript's text item delimiters to ""

	repeat with letter in thePass
		if (letter = "0") then
			sysKeyCode(29)
		else if (letter = "1") then
			sysKeyCode(18)
		else if (letter = "2") then
			sysKeyCode(19)
		else if (letter = "3") then
			sysKeyCode(20)
		else if (letter = "4") then
			sysKeyCode(21)
		else if (letter = "5") then
			sysKeyCode(23)
		else if (letter = "6") then
			sysKeyCode(24)
		else if (letter = "7") then
			sysKeyCode(26)
		else if (letter = "8") then
			sysKeyCode(28)
		else if (letter = "9") then
			sysKeyCode(25)
		else if (letter = ".") then
			sysKeycode(47)
		else
			sysKeyStroke(letter)
		end if
		delay 0.1
	end repeat
end sendString


set oldPassword to system attribute "OLDPASS"
set newPassword to system attribute "NEWPASS"

activate application "WorkSpaces"
	sendString(oldPassword)
	sysKeyStroke (ASCII character 9)
	sendString(newPassword)
	sysKeyStroke(ASCII character 9)
	sendString(newPassWord)
end activate