more than one instance of SoftwareI2CLibrary ? - possible ?

Is it somehow possible (without rewriting the library) to init it more than one time? I have the option between using a mux, or just using more pins for more I2C busses.

(Need to address 5 devices that use the same I2C address) - if it's trivial, I'd like to load five instances of the SoftwareI2CLibrary for different SDA/SCL pairs..

No. Not possible without a massive re-write. The constants you define before including the library are used to hard-code register addresses into assembler functions. You would need to generate new names for each of the assembler functions for each instance.

There are devices called I2C Multiplexers that allow an I2C port to fan out to multiple I2C busses that each have separate addresses. Perhaps that is a way to solve your problem.

Thanks for the answer related to library, I am familiar with PCA9548A so the hardware solution is not a problem. (just a matter of spending a IC & 10 more resistors :)