Unfortunately this is not supported for morphs in way your are wanting. It is also not supported for hair and clothing. If you have no "morphs" root key in the save file, and setUnlistedParamsToDefault set to false, then it will leave morphs as is when loading that preset. If you have a "morphs" key in the save file, it resets all other morphs, regardless of how setUnlistedParamsToDefault is set. That was the intended function here, although it makes more sense in something like an appearance preset which has multiple root keys. Support for what you want could be added, but I think it would need an additional key, like "resetMorphs", to indicate what to do. The reason is there could be a case where you have an appearance preset you customized by setting setUnlistedParamsToDefault to false and removed another key, like "clothing", but still have the "morphs" key present. In most cases, people want the listed set of morphs there to be the complete set that is applied, and not treat as a merge.