It's definitely worth knowing how much lengthening the tail affects the CG location, and as Rock notes, it's easy to do.

It's also possible that the previous location was more conservative than it needed to be. Model designers do this all the time. People set the CG and don't experiment, so they never find out. Before the changes, perhaps the plane was easy to balance, and it flew well, so there was no issue. Now there IS an issue.

I do this calculation for every plane I build. It often saves me the hassle of trying to move equipment around or finding places to add weights. Why add more weight to the nose than you need to?

Jim