Hi gtrue1978
Yes. Your understanding is correct. I am afraid it is not possible to change the slave address of ADE7878A. Can you choose an MCU with two I2C ports? Or can you consider the option for setting up a software (bit-banging) I2C communication setup?
Please have a look at this post: (this is the same post in which an I2C mux option was suggested to Tim-S for ADE7816). ADE7878A is very much similar to ADE7816 in this respect.
Regards
hmani