Beanie had another vet checkup today to see how the tumour is going. The vet said it _might_ be very marginally harder (softer is better) but it's really subjective, and Beanie wasn't reacting at all to all the poking and prodding. They did a blood test and they were 100% perfect, and his weight has been completely stable as well.
We're going to stick with the original plan of getting another CT scan done in December because the vet said she wasn't concerned with how everything was looking right now.