I"m glad your trophy LMB didn't die from the prior catch, and I hope he/she lives for many, many more years.

If you value his/her genetics, then your core desire is to put the least possible amount of stress on that fish in any/all activity with it.

One suggestion is to tare your carry bag, and then weigh the fish in the bag. Just less stress overall while still getting the weight.

Whether or not tossing him/her back in the water is best for the fish...who knows?

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."