Hi Raghu,
No, and I can't understand why it seems different from VDB... the main difference is citric acid instead of tartaric. Despite what Namias wrote, I tried a few different toners, both before and after fixing. I'm not at home right now so I don't have my notes, but off the top of my head I remember trying Clerc's gold toner ( I think that's the one with some thiourea? -- anyway it was a thiourea gold toner ), gold and platinum toners made with weak citric acid, and gold toner made with ammonium thiocyanate. I was able to get shifts in image color but they were weak and tended to make the image lighter ( the platinum toners left a silvery image whether done before or after fixing... leaving a weak image without strong darks ). I also tried combinations too without much success. Nothing execpt gold thiocyanate looked very good.
I can confirm that for me, ammonium thiocyanate gold toner worked well both before and after fixing, which does not match what Namias wrote. I couldn't see much difference between the two, so it made the most sense cost-wise to wait until the image was fixed and dried and then decide if it was worth toning it. I came to think when Namias wrote "to an appreciable extent" he meant to darken or to change in a desireable way. I'll be home in a couple months and can post some examples if you are interested.
Actually, that's not the only mystery. I've used this process a lot to make "negatives" to then make cyanotype positives. I have a large number of these negatives that were "fixed" with just sodium sulfite, and none of them show signs of deteriorating. I also have a few that were "fixed" with sodium chloride, which leaves an interesting yellowish-gold image, and those haven't faded either. "Fixing" definitely does not mean the same thing as it does when silver nitrate is the light sensitive component! I have wondered if "fixing" in thiosulfate is also a kind of sulfur toning, since there appears to be intensification of the image.