I don't know the details myself. History in general was pretty high on the list of Things Not to Be Discussed in the Interest of Galactic Harmony And Polite Conversation, and that went double for the history of technology.
My personal take, without much evidence, is that this was perhaps less dangerous than you might expect. Morphing is based around rapid regeneration, which is probably something they developed (or discovered. It's wild on good old mater terra, and possibly even natural, but now I'm getting off topic.) before the rest of the technology. That provides a reasonably good fail-safe (though with a long-term risk of cancer if they don't come up with some way to turn it off). Then, just tie that into a psychosomatics and z-space attachment and hey-presto! There's morphing.
But the painkilling is something they must have developed later. They definitely had regressions on that front as they tried to improve the technology.