pick1e:
But how do I access its registers and EEPROM?
Exactly the same way you do with an Arduino board...
The ATtiny85 datasheet also has good C examples of register access.
The first thing I need this for is to set pin 1 as an I/O pin rather than RESET.
Once you do that you can only program the processor using a high-voltage programmer or a bootloader.
I assume I need to set a register value but I have no idea how I'd access it.
No. You change a "fuse bit".