Since last post I've used up three quarts of emulsion from the original gallon and just mixed last one a few days ago. I have experienced no issues with this method - screens burned great and relatively consistantly. I wanted to be sure that splitting didn't mess anything up before posting again. Ulano 925WR does everything I want it to but ships with liquid diazo, so it is hard to split but not impossible.
The full weight of the plastic diazo bottle the gallon comes with is 2 1/8th oz. The bottle is 3/4 oz. empty so that means the diazo in the container is 1 3/8 (1.375) oz or thereabouts. The diazo must be divided into four parts - to do this cut the diazo bottle open with a a knife so you can scrape all of the goo out with something, maybe a plastic knife or spoon. I did this in a darkroom with safelights on - unsure if this matters with raw diazo liquid. I used 35mm film canisters to store the split diazo. Use a small scale and scrape out 11/32 (.344) oz. of diazo into each of the canisters.
Figured the included diazo bottle holds around 8 oz of water when filled to the specified point, so 2 oz of water is poured in the film canisters when you're ready to mix which is just about to the top. Works out! Sometimes not all of the diazo mixes with the water when you shake it so take advantage of the open top of the canisters and mix it a little so everything incorporates.
Kept the canisters on top of the emulsion pail. I think it has been about eight months, and each newly mixed quart exposed with the same time and performed identically. I was worried that exposure to a lot of air when scraping the diazo might mess it up but I guess it didn't.
Also, remember diazo stains everything it touches so put some plastic down or something.