You can change the values around on the plate and the cathode, but in general they need to be changed together. I have a certain Plate/Cathode resistor level that I like in the boutique amps we are building. You have to be careful as they are changing the current in the tube. But if you get a 12AX7 data sheet, you can calculate the values necessary for what you want. For more gain, you might try 220K which is a common Plate value on High Gain amplifiers. I went lower on one amp to give a bit more headroom. Wanted it to break up at higher levels.
Make sure you learn about load lines and practice some Ohms law if you want to play around.