Mark you said: However I don't believe this is a practical way of doing anything with AI since some of the assumptions might not hold and the underlying function is much more complicated than y = ax + b
I agree that those assumptions might not hold.
I'm not sure what you mean by saying you can change the indicator's length from 30 days to 14 days, but if you provide an example, I'll try to add some comments.
If you look at a price chart with any indicator MACD RSI Bollinger Bands and change the indicator settings 30days to 14 days or to whatever gives you the best signals that's curve fitting.