Thanks! I'm glad one of us knows what we're doing around here! :-)
I did find a second sort of "kludge" for the problem -- not sure I'd class it as a workaround, because I don't now if it works for everyone, across the board, but it has helped me to get clones into my game in another way, besides merging households with the Scientist character, and without the need for hacking or other off-the-books program modification.
As above you can still clone Sims who are a part of the Lvl 10 Scientist's household, provided he or she has built and upgraded a Cloning Machine.
Problem is, if you're playing a game where your cloning target is not simply some random townie, but a Sim who's part of another significant household you're currently playing in your world, merging that Sim's household (even temporarily) with the Scientist's can really alter the status quo for the target Sim's household.
So here's another way of handling it that I discovered last night while attempting to use Maxis' George L'Ernitage (my Level 10 Scientist with an upgraded Cloning machine in his inventory) to clone Bella Goth.
In my game, Mortimer has divorced Bella, meaning that it's just Bella and the kids at their family home of Ophelia Villa.
I couldn't just merge Bella temporarily into George's household, because the game wouldn't allow me to leave the kids behind unsupervised (pesky kids!) -- but if I merged Bella and the kids with George's household, even temporarily, the game would count this as the Goth family "moving out" of their home -- and I would lose all the custom decorating and other progress I'd already put in while playing the Goths.
Not the desired effect.
So, here's what I did.
NOTE TO ANYONE READING -- MAKE NUMEROUS MANUAL SAVES (AND TEST THEM!) WHILE TRYING THIS, SO THAT IF SOMETHING GOES WRONG, YOU CAN ALWAYS GO BACK TO WHAT YOU HAD BEFORE!!!
Sorry for "shouting" but I would hate for anyone to lose a long-running Sim Town because they missed that bit!
Okay, so what I did --
Playing Scientist George, I had him go to visit his friend Bella Goth at Ophelia Villa while she and the kids were home.
While at the Goth house, I took the upgraded Cloning Machine out of George's inventory and put it in the back yard of the house.
I had George go play a game of chess with young Alex.
I made a manual save (To do this -- type in a save name in the field provided, and click the button on the lower right -- when you see the swirling animation, it means it's saving. Test it by loading the save afterwards, if you're not sure it worked).
After I made the manual save as George visiting the Goths, I went to the Manage Worlds screen. I did not save again when the game asked me, because I'd just made a save of my own.
From the Manage Worlds screen, I immediately loaded the Goth household.
George was still there, where I'd left him, and the Cloning Machine was still in the back yard, but now I was control of the Goths, not George.
I had Bella go out into the back yard by the Cloning Machine, and I made a new manual save right there, under another new name (and you should too :-) )
Next I had Bella (not George) activate the "Clone Sim" function on the machine, and choose herself as the target.
The cloning worked (!), and Bella's new clone was now a part of the Goth household.
I made another manual save here, under a new name, and returned to the Manage Worlds screen (again, I didn't save game when it asked me, because I just did this manually)
I clicked on George's house to begin playing him -- since he was currently at the Goth's, his house portrait was grey.
When the game loaded up, I was once again controlling George -- who was still at the Goth's with Bella and her new clone. I put the Cloning Machine in George's inventory, and had him travel home.
Once George was home, I made a new manual save for him, then I loaded up the Goth house from Manage Worlds and started playing with Bella and her new clone.
All good.
I apologize for this long and pedantic write up, but I didn't want to skip any steps, because I didn't want anyone reading to accidentally screw up their game progress by saving in the wrong way, and/or at the wrong time.
Hopefully, this "kludge" will allow people to create clones in their games, without merging households, until the Cloning Machine bug is officially fixed.
That's all. Thanks for your patience. Have fun!
