Question: Is there a way to read and write to an EZ-USB memory (AN21xx/FX/FX1/FX2/FX2LP) device?
You can use the A0 vendor command to read and write to the internal memory of EZ-USB (AN21xx/FX/FX1/FX2/FX2LP). For this vendor command to work, the CPU of the device must be in reset. To put the CPU in reset, send the A0 vendor command with E600 (for FX1/FX2/FX2LP; for older parts like FX use 7F92) as value and 01 as data. To bring the CPU out of reset, send 00 as data.
For reading and writing to the external memory you can download vend_ax example to the device, and then use the A3 vendor command. Both these vendor commands use Value field to specify the memory location.