I don't think adding weights to a "rim" in a turbine is a normal procedure, I think that would be a bit crude.
fleigle,
You say it was many years ago, but today the allowable unbalance levels on rotors are so low that what you saw (weighing and distributing in best pattern) is today only the first step because it is no longer good enough to meet the low levels of unbalance required to prevent, for example, unacceptable noise levels in the aircraft. The next step is to actually measure the unbalance by spinning the rotor on a balancing machine. The machine then says what balancing weights are required in what positions on the rims.
So, the initial assembly, although done with the utmost precision and dedication, has to be fine-tuned with balance weights, since as is the general way of the world we are always demanding something today that's better than yesterday.
pk