As Skylark-flier indicated for those admittedly rare times it may be necessary to add lead to the tail there are an infinite variety of ways to do. Really almost case by case for each airplane.

Please allow me to tell of one such solution that I came up with some years back. I was setting up a pair of Messerschmidt 109's for my team mate and I to use for warbird pylon racing. I wanted to do some fine tuning of the CG and all the internal options were done. Weight added back at the tail would be minimal for this fine tuning but where to put it?

Well fortunately these airplanes were 109E models and had scale struts from the bottom of the fuselatge up to the bottom of the horizontal stabilizer, Hmmm? so got out my little chunk of railroad track and the the small ballpen along with some assorted fishing weights and wheel balancing weights. Hammered one of the weights totally flat and almost paper thin on the anvil (chunk of railroad track).

Next step was just to cut the thin sheet of lead with scissors to a size that would balance the airplane right where I wanted it to and then it was just wrapped around the strut or struts neatly with a small squirt of thin CA. Worked well and looked very scale.

Just one of many ways to approach the problem

John