change I2C speed WITHOUT modifying library?

Projects Networking, Protocols, and Devices
2

This code sequence should give you the current frequency.

uint32_t prescaler = 4 ^ (TWSR & 0x03);
uint32_t freq = 16000000L / (16 + 2 * TWBR * prescaler);

I don't see a possibility to get that frequency at compile time.

To set a frequency of 400k use:

TWSR &= 0xFC;
TWBR = 12;