Can anyone think of a reason why it would be a problem to perform a diacetyl rest AFTER primary fermentation, secondary fermentation, and a period of lagering have occurred? My idea is that after lagering for about 3 weeks, I would warm the beer up to about 55 degrees and add one or two fresh Activator packs. My assumption is that the fresh yeast should mop up any residual by-products (diacetyl, acetylaldehyde) that the primary and secondary fermentations did not reduce. After this fresh yeast had done its work (maybe 5 days or so), I would crash cool back to lagering temps and finish lagering for another month or so, flushing any flocculent yeast from the conical as necessary.

I know that this may seem like a waste of money for the additional yeast, but I don't like the idea of (1) having to catch the fermentation at exactly the right time in order to warm it up for a diacetyl rest (because this risks either warming it up too early and generating undesirable by-products or warming it up too late and achieving an insufficient clean-up) and (2) I wonder if the yeast that are still in suspension towards the end of fermentation are sufficiently viable and numerous to perform a successful clean-up.

My main concern about this technique is that, lacking additional fermentables and being pitched into a high-ethanol environment, the fresh yeast would be like "screw you guys, I'm going home" and would flocculate to the bottom without doing any work.