Just figured I'd share an unplanned successful disaster.
I had brewed and bottled a blonde ale that I was very fond of a few months ago but I thought it was a little light on flavor for my taste. Normal commercial beer drinkers loved it so I decided to brew two five gallon recipes, one with the same measurements as the first "the people pleaser" and one that was a little heavier on everything to see if I liked it better. Another friend joined and brewed a nut brown. (15 gallons of three different beers brewed in a one bedroom apartment, sometimes I love extract brewing)
All three sat three weeks in primary then "the people pleaser" went into a keg, force carbed, and was drinking three days later. Waited another week for my friend to become available so we could bottle his nut brown and my other blonde at the same time. When he showed up he realized he had forgotten all of his bottles. We looked and knew we would be close but should have enough of my bottles for both batches.
Bottled his just fine but ran out of bottles about 2.5 gallons into mine. That was just way too much beer to dump so I opened up my keg of "the people pleaser" and had noticed that it was about half way gone so I decided to rack the 2.5 gallons that was left right on top.
Basically I took 2.5 gallons of force carbed beer and racked 2.5 gallons of sugar primed beer right into it. Force carbed again using 20psi keeping a close taste on the carb levels.
All has turned out just fine. I just make sure to keep an eye on the psi and purge every once and a while since the sugar in the one intended for bottles is probably raising the psi slightly each day. Granted this only worked because they were basically the same beer but I thought I'd share.