The firm of Hill in London make a peg paste in a lipatick like dispenser which is smooth but the pegs don't slip. I favour it. Hidersine make a compound in a black block but it seems to hold more than allow to turn. Rosin used on the pegs melts and tends to slip in extremes of heat in outdoor playing.
I have seen a tool called a reamer, in the hands of an Australian violin maker, which cuts a correct tapered hole in either side of the peg box.
If a hole becomes too big for a normal sized peg, some repairman prepare a collar or grommet or bobbin of new wood, which is prepared into the side of the peg box, and using a reamer cut a standard sized tapered hole to last for the next few generations. This is less obvious if your do four at a time. The tone is not affected.
For some this would detract from the value of a fine fiddle. I myself don't think so.
I had nice fiddle which used African Monkey Pod wood pegs (I think!) which were ornately finished. I went to display the fiddle at the Australian Musical Instrument Makers annual show. They were hopeless in the heat slipping all the time, and I had to prevail on the maker to give me simpler pegs of a different wood with which I have been very happy- I bought the fiddle.