In years past, tuning wasn't all ECU based. I myself fooled my ECU for years until I could get a proper tune on the car. I understood what the car was doing in stock form, I somewhat knew how to fool it and I took steps to make sure I wasn't doing too much harm to it.
There are always ways to tune W/O computer intervention. You just have to play on the failure limitations in the factory programming, generally 25%+/-. But shooting lower would be safer, say 10-15%+/-.
How do MAFS work?
How do injectors work?
How do spark plugs work?
There are ways to tune every car if you understand.