I had been searching for this item for years. Finally I discovered someone who makes it. Unfortunately it's kind of expensive. I even went so far as to do a patent search to see if anyone was building something like this.
I was thinking it would be great to have something that worked as an adapter to allow you to use an octal tube in a socket wired to accept 9 pins. A common application would be to use a 6V6 tube in an amp wired to take EL84 tubes.
My main reason for wanting this would be to convert an amp that required 6973 tubes to use 6V6 tubes. 6973 tubes are very expensive NOS and there's only on modern manufacturer making them (Electro Harmonix)
You'd have to rewire the pins and totally replace the sockets. on top of that you have to cut larger holes in the chassis to accept those sockets. That would totally devalue a vintage amp. and probably cost hundreds of dollars.