The baby swing from the Store is a wonderful object for those who like to play toddlers and also is a nice alternative to having babies in the crib 24/7. But why in the world did they make it a "magical" object ?!
I was disappointed that all the baby/toddler motives go up when in the swing, making it useless to even care for the little one. So I decided to mod it myself.

I opened the package and looked for the ITUN instance corresponding to the interaction Be In Swing, planning to edit the numbers in the output section... except there are no such ITUN file. There is an ITUN file for BabySwing+Swinging but the output section is blank.

There is no _XML instance relating to the baby swing either. I also looked in GameplayData.package with no luck.

Anybody know where to find the files pertaining to the motive gain while in the swing? Any help would be greatly appreciated!

In that case the tradeoff may be hardcoded. I don't have that object and it's not part of the Sims3StoreObjects assembly that come with a recent patch, so I can't investigate.

If you can read code, extract the S3SA resource, open it in an assembly browser like ILSpy or .NET Reflector and look if you can identify where/if the tradeoff is implemented there.

Thank you very much, Buzzler, for your answer. If I understand correctly, from what you said, it seems that I'll need a script mod to change the output of the interaction on the motives? Well, I will try looking into what you are suggesting next weekend once I have access to a PC (I play on a mac and mono makes for very unstable applications, at best). But unfortunately, I have no coding background so this seems totally out of my skill set at the moment, the best I achieved so far are simple XML or ITUN tuning mods (with a 50% success rate on the ITUN mods); I may have to give up on this one!