I am currently working on a highchair which is turned round 90° and moved half a tile to the left, while keeping the original footprint. This should enable toddlers to eat at a dining table with the rest of the family. Basically, I did it, but now I'm stuck on fine tuning, and would be glad for help.
I edited the RIG-resource to move the chair, namely the “offsetBone” part of it (I tried all the others, but only this one had any effect). I also moved all the slots where I wanted them to be, but moving them didn't have any effect at all.

Now what happens is the following:
When I place the highchair, it appears just as untweaked highchair standing on its footprint, facing ahead (the wood-pattern on the screenshot shows the footprint).
When a Sim starts putting a toddler into the chair, it snaps into the new position immediately, facing the table. But the toddler is still being put into the old position, until the seating interaction is finished. Then it snaps into the new position, too. The parent's arms follow the toddler, and the highchairtable.
Now the toddler is sitting at the table (that's the part I'm already quite happy with!)
Parents can serve food and bottles, but their arm-movement is looking extremely unhealthy, especially with the bottle.
Also, the toddler is holding the bottle too high up. I promise, I haven't altered any component's height.
When the child is taken out, the snapping occurs in reverse order: first the toddler snaps back, then the chair.

So what I would like to do, is to adjust the animation to a sort of compromise between looking natural and being a bit off. Having child and chair in the new place, all the time would make this much easier. I also would like the parent's hands to act as if it were a normal highchair, but with the food perferably appearing in front of the child.
I did read menaceman's thread about hand-positioning with the stylist-station, but it only got me so far. I couldn't find any IK-joint in the highchair's RIG. Everything seems to depend on this “offsetBone”; chair, toddler, bowl, bottle and hands. Is it even possible, to alter some of these individually?
I'd be grateful if anyone could help me, or at least tell me it's impossible, so I can stop worrying about it.

You best rotate the whole chair by rotating the transformbone(in the RIG), after that experiment with the routing slots as those will have effect on the sims position when the animations start.

I tried it, but as soon as I rotate the transform-bone instead of the offset-bone, there is no rotation at all, ingame. Similar with the routing slots: Moving them was the first thing I did, and it works with the mother's position. As you can see in my screenshots, I moved her half a tile towards the table. In fact, when I took the pictures, the toddler-slot was at the table, and the food-tray-slot was at the sitting toddler's right side. They just ignore them!

Then stick to the offset joint and routing slots

Hey, just writing to say thank you. Actually yes, it was impossible, but your suggestion has pointed me towards a solution without rotation (I moved the mother, instead of the chair).