jeez, nothing personal hail don't get mad but I need to correct this situation.
the PROPER way to do this is to use a strut socket and an allen (hex) socket. you can see a hex/torx socket in the top of the strut rod. DO NOT loosen it while it's on the car, you are in great danger if you do this because the spring is under pressure and could fly off and take your face out. besides, even if it's still on the car the strut rod will spin.
the style below, you use an open end on the top of the socket and stick an allen key in the top where the 3/4 drive would normally go into the torx on the top of the strut rod. now use a box wrench to get more torque with the allen key. loosen the nut using the open end/socket.
now, another method is using an impact gun and getting a good grip on the strut mount/bearing. I don't bother with the strut socket personally, but spinning the strut rod is not good for the valve at all. no harm done so far but I only trust myself with it.
and to answer your question, it is not completely necessary to replace the top nut, but it is a known thing that if you have a lock type nut with the plastic ring at the top, it's supposed to be a one time use. the plastic weakens every time you remove it.
if you're alright with re-using it which in my opinion isn't that half assed, just use a little loc-tite blue or a tiny dot of red.