A few things that i notice with your json;
default_value can never have a python function, use value instead.
Things that need to be evaluated by python (such as; 5 if machine_type == \"A\" else 3 if machine_type == \"B\" else 9) need to be enclosed by ""
default_value must be a part of a setting.
So if you take that into account, the json would be someting like
"input_paramA":
{
"label": "Second JSON",
"description": "Beep bop boop",
"unit": "mm",
"type": "float",
"default_value": 5,
"value": "5 if machine_type == \"A\" else 3 if machine_type == \"B\" else 9"
}