There are two bits to the variant from Conques. The first variant cuts off to the left soon after you climb out of Conques. I did take this- it passes near Noailhac. I took it as I heard it had some spectacular views, but I hadn't been on it long before the mist came down, and I saw nothing. Then a thunderstorm arrived, and the rain poured down. (It turned into my 'day from hell' for a variety of reasons actually- makes a good story in hindsight, but not at the time!) There weren't a lot of markings on this variant, but enough so you didn't get lost, and it rejoined the GR65 not far from where the other shortcut towards Livinhac leaves the GR.
I didn't take the second bit of the variant (to avoid Decazeville) mainly because it was raining so hard where the routes diverged that I couldn't get my MMDD maps out of my bag to look at properly. So I decided to take the 'main' route. I arrived at Saint-Roch where the routes join together again looking like a drowned rat- while a couple of people strolled along easily from the direction of Agnac, looking quite relaxed.) It was also a steep, sloshy muddy descent in the wet conditions after Saint-Roch down to Livinhac, and I didn't meet anyone else much on the descent. I suspect French-speakers might have acquired more local knowledge and perhaps went a little to the right at Saint-Roch to take the D21 road downhill towards Livinhac, given the wet conditions.
Margaret