I've been looking at I2C RTC modules like this one, but they all appear to be normally connected to pins 1,3,5,7,9. However, I'd also like to try to use a RaZberry Z-wave module on the same Rasberry Pi, which uses all of pins 1-10. Is there any way to reconfigure pins 19,21,23 (SPI pins?) to work with the RTC module? Pins 17 and 25 look like they are already the power and ground you would need.
You could bit bang I2C on any spare gpios, so you could use the RTC on other gpios.
However I expect you want the RTC module to automatically assign the time to the Pi when it is booted. To do that it must be connected to I2C bus 1 (gpios 2 and 3 on pins 3 and 5).
I2C is a bus so more than one device may be connected at a time as long as there is no conflicting gpio usage. You would need to ensure that the z-wave module either does not use gpios 2 and 3 or uses them as the I2C bus.
Your next problem would be connecting an RTC to the gpios. I suppose you could solder wires to the underside of the pins on the bottom of the board so leaving the top free for the z-wave module.
i2c-gpio and i2c-rtc-gpio are now valid options. Maybe you could check documentation for these overlays.