There are actually two different problems discussed here.
One is Sims constantly beeing in a happy mood (which can be changed by using mods like RoBurky's True Happiness mod or any happybuffschangedtofine mod (e.g. http://modthesims.info/download.php?t=579603 and if one wants to go even further additionally lesshappyfoodanddrink and/or laundy buffs fix)
The other one are overtoned facial expressions (which has already been discussed in this thread
https://forums.thesims.com/en_US/discussion/822154/please-adjust-the-ear-to-ear-happy-smile/p1
can be fixed by using mods like Shimrods Facial Overlay mod
http://modthesims.info/download.php?t=574482
or a similar mod like my lessfacialoveraction
https://deichschafblog.de/bienchen/sonstige-mods-misc-mods/)
