gistfile1.rb

default = {
  "key1" => "val1",
  "key2" => "val2",
  "key3" => {
    "1" => "one",
    "2" => "two" 
  },
  "key4" => "four"
}
custom = {
  "key1" => "val1",
  "key2" => "newval",
  "key3" => {
    "1" => "one",
    "2" => "too"
  }
}

result = default.merge custom

# >> result
# => {"key1"=>"val1", "key2"=>"newval", "key3"=>{"1"=>"one", "2"=>"too"}, "key4"=>"four"}