How to Set Up Sync of two mysql databases without master slave
You can use any of the available ETL Tools:


Talend
Pentaho
others, like Informatica 


Initial size not important, the most important is the daily number of changes.

You will need to add a timestamp for INSERT/UPDATE or a bit column and triggers to mark the new sync status.

My clients sync millions-row databases (DB2/MySQL/Web) by cron jobs.

An other solution may be SymmetricDS (read the article about transformation of data using it: http://www.symmetricds.org/doc/3.0/html-single/user-guide.html#transform-data).