Catalina already introduces a new concept: A disk partition for system files (read-only) and a disk partition for data files (writable). Any boot-sector magic you choose would need to survive any upgrading to Catalina (assuming you go to Catalina or beyond) AND any Catalina upgrade would need to recognize the partitioning to start (which it may not).
Perhaps you may want to start a thread in Catalina forum asking about those effects (or this thread could be relocated to get the right attention).
I suggest you should find a way to fix the issues you currently have, or try another VM product that may be more stable.
I will bow out after this because I just stated what I would consider a best approach based on my knowledge of OSX.