Understanding serial JSON API for provisioning

I am working on my own (hardware) flasher for WLED and it is going well. Happy to share the project h/w and s/w (all on GitHub).

I see the Serial interface works, and has a JSON API (I can send {“v”:true} and get a reply).

I see the Serial handles IMPROV which works and I can get info and set WiFi SSID/pass, which all works.

Is there any way, presumably JSON API, to set config for GPIOs? Ideally I want to make different manifests on my flasher for specific boards.

I tried sending the whole cfg.json but no luck.

I’d rather not flash an initial SPIFFS image if I can avoid it as a proper API would be neater.

I hope I am just missing the obvious. Thanks.

FYI:Flashing a snapshot of SPIFFs does work, but somewhat messy way to do it (and esp_serial_flasher had a bug that stopped me doing that as it goes to end of flash).

It would be nice if there was a proper way to send cfg.json via serial API please.