Frankly, today the way to do this is to encapsulate the functionality in Docker containers rather than modify the standard DSM environment. The beauty of Docker on DSM is that you can extend Synology filesystem access (and speed) directly into the container so there really is no performance downside. If that interests you, you could easily do all your Docker dev/test in XPenology and then have very high confidence it would function exactly the same ported over to other DSM versions and Syno platforms.
I used to run optware and never had any real issues (other than a version upgrade overwriting the optware startup, which was easy to restore). Since it installs it's own package versions in its own directory tree, and because the standard shell doesn't have optware enabled, compatibility seemed to work out pretty well for upgrades. But again, I've pretty much moved all the things I wanted to do in the native shell/optware to Docker and won't look back now.
That said, I'd be confident of using XPenology to model out your upgrade and functionality plan. Again, I never encountered problems with upgrading due to optware excepting the rc entries to start optware. However, that advice is worth exactly what you paid for it
Good luck.