It depends on the tech guy.
We just did an event with a new cage last weekend. Before heading down to Memphis we called and asked the tech folks whether it would be a new log book or they would note the new cage in the current book. We got both answers.
So we headed down with the old log book - told them what we had done (removed bolt in cage, installed weld in cage, changing tube size along the way) - and let them decide how they wanted to handle it.
They changed the cage notes in my existing book, completed our annual tech and we were on our way.