Can i adjust the Gem's Spawn rate? Done

Yes, you can.

Set "Use external YAML file" to on in the Jewelcrafting config. Then create a file called Jewelcrafting.Sockets.yml in your config folder, paste this in:

gems:
  meadows:
    green: 0.43
    black: 0.01
    purple: 0.01
    blue: 0.01
    yellow: 0.01
    red: 0.01
    orange: 0.01
    white: 0.01
  black forest:
    green: 0.01
    black: 0.43
    purple: 0.01
    blue: 0.01
    yellow: 0.01
    red: 0.01
    orange: 0.01
    white: 0.01
  swamp:
    green: 0.01
    black: 0.01
    purple: 0.43
    blue: 0.01
    yellow: 0.01
    red: 0.01
    orange: 0.01
    white: 0.01
  mountain:
    green: 0.01
    black: 0.01
    purple: 0.01
    blue: 0.43
    yellow: 0.01
    red: 0.01
    orange: 0.01
    white: 0.01
  plains:
    green: 0.01
    black: 0.01
    purple: 0.01
    blue: 0.01
    yellow: 0.43
    red: 0.01
    orange: 0.01
    white: 0.01
  mistlands:
    green: 0.01
    black: 0.01
    purple: 0.01
    blue: 0.01
    yellow: 0.01
    red: 0.01
    orange: 0.43
    white: 0.01
  ash lands:
    green: 0.01
    black: 0.01
    purple: 0.01
    blue: 0.01
    yellow: 0.01
    red: 0.43
    orange: 0.01
    white: 0.01
  deep north:
    green: 0.01
    black: 0.01
    purple: 0.01
    blue: 0.01
    yellow: 0.01
    red: 0.01
    orange: 0.01
    white: 0.43

Then adjust the numbers to your liking and save the file. The world adjust in real time, no restart or anything needed.