The problem with bulk fares often doesn't lie with the restrictions themselves, but the capacity that the consolidator has been granted by the airline. For example, say you bought a consolidator ticket as a "T" class (generally one of the lowest of the low airfare classes). If you bought it and the airline then closes out the consolidator's "bucket," you won't be able to change it, even if the airline still has "T" class tickets of its own to sell. IF the consolidator has similarly restricted tickets like "L" or "K" class, you might be able to swap them, through your agent, but only if the consolidator's window is still open.
Similarly, say you bought a discounted "Q" class ticket directly from the airline. If you wanted to change it and that particular class was sold out, you could ask the airline to let you pay the difference and a penalty to upgrade to a full-fare, unrestricted "Y" class ticket. You won't be able to do that with a consolidator fare. The other restriction you'll find across the board: You'll never be able to upgrade your ticket using miles. The lesson: You'd better be sure that your consolidator ticket is the one you want, because you're most likely stuck with it.