So we've realized that a) there's never been a clear in-book rules citation that says this is categorically possible or impossible, and b) we've said over and over on the forums that it can't be done.
At the same time, there's never been a reason why it can't be done, just arbitrary pronouncements (everyone by this point knows the term "Omnismoke"), and we have a handful of Clan mechs that were refit at the factory level into omnis or otherwise played around with.
So, we're leaving most of the rules as they are. Most notably, the main procedure as detailed in TM remains unchanged: nominate fixed equipment, and that can't be altered in standard omni configs. Where we're introducing a tiny bit of flexibility is in the StratOps customization process. Those rules are being revised, because they've generated a lot of confusion over the years. One of the numerous changes in the revised version is that it will be possible to alter fixed equipment (either to other fixed equipment, or to more pod space) as a Class F refit (i.e. factory-level, impossible in the field). This makes the statement from SO p. 189 that you quoted actually doable by the rules.