Board without ethernet and current control

Hi! I’m building a custom board without ethernet and current control. I need to build a special version of the firmware, or enough to make changes in the configuration file? Ethernet and i2c for current control lines can be left nowhere connected? Can I use these lines for my purposes?

Imported from wikidot

You can de-activate both in the configuration file.
You can re-use the I2C pins, but not the Ethernet pins.