The last sentence seems wrong. If you are actively breaking the law, you aren't supposed to be able to solve that problem by registering. OTOH, not sure what "active lawbreaking" was considered to be there. What is registerable is a so-called bullet button rifle. But these are currently legal to possess. They could be legally owned, purchased, assembled, etc., up through 12/31/2016. At 01/01/2017, you could no longer legally purchase or assemble one but it's not against the law to own one in California. Basically there is a year in which to decide what to do with "bullet buttons," as in register, convert to a compliant form (featureless, maglocks requiring disassembly, etc.), dispose of out of state, etc. They aren't going to let you register incomplete rifles, as in receivers, boxes of parts, etc., that aren't yet complete "bullet button" configurations because you aren't able to legally build a new "bullet button." But, again, owning un-assembled parts, receivers, etc., is not illegal because there are numerous ways to assemble them into compliant configurations that don't require registration.
Now, come 12/31/2017, if you haven't registered, converted, etc., then a tick of the clock will change legal status, but that's then, not now.