Hi @BAW ,
Please read this application note:
AN13460:
https://www.nxp.com/docs/en/application-note/AN13460.pdf

So, you can find it is supporting the ISP, which is the USB HID method to download the code.
In fact, you can consider it is using the flashloader function, just put the flashloader from RAM to the flash to realize the USB HID ISP method.
So, answer your questions again:
1. SBL support USB HID updates
2.what would need to be done in the flexSPI interface?
=>Answer: The SBL is using the RT1020 which is the external QSPI, RT1024 is the internal QSPI, so the flexSPI interface pin is not the same.
This is the RT1024 situation:

This is the RT1020 situation:

So, you need to modify the RT1020 code flexSPI pin to the RT1024 pin, otherwise, RT1024 can't work.
To the SDK, in fact the flashloader support the USB HID, just this code is run in the internal RAM, if you want to use it as the secondary bootloader, you need to download it to the flash, then copy it to the internal RAM to run it:
SDK_2_14_0_MIMXRT1024-EVK\boards\evkmimxrt1024\bootloader_examples\flashloader
Wish it helps you!
Best Regards,
kerry