Benzotriazole works as an anti-fogging agent (and also used to be used to cool down warm-tone papers back in my youth). To make a working solution dissolve 2g of Benzotriazole in 500ml of water at 125°f/52°c or higher and then add water to make 1 Litre of working solution.
Using small test strips, add 8ml of the working solution per litre to the developer and repeat until the fogging is no longer apparent.
"how is it different from overprinting in combination with reduced development?"
If you overexpose and under-develop you will get a shift in colour and your dark tones and blacks will be very week (will look too grey).
"And is there a practical maximum on the amount of benzo to add to the developer?"
The practical maximum will be determined by the type of paper and the level of fogging. You have to find this out yourself through empirical tests - just bear in mind that Benzotriazole is a great additive that does it's job very well but it can't work miracles.
Bests,
David.
www.dsallen.de