FW, but you can't replace reported RVR with pilot assessment if any of the RVRs are below take off minima.
We can. And do, certainly in the sim. In real life the airport generally grinds to a stop with that kind of vis.
If I was given RVRs of 50/75/50 at LGW, from A/A3 (the 15m spacing is a separate discussion) and I assessed the TDZ visibility as 75m or more, I could take off, according to our manual. What other operators do, I don't know but I've done this with the CAA in the back with no complaint...