In previous versions of Optifine that supported CIT models, using "texture=" for an item using a custom generated style model would override the texture specified in the .json file. This doesn't seem to work in 1.13.1. The texture in the .json file will take priority instead.
Both resource packs will apply a custom texture and model to a diamond sword named "Diamond Spear". The 1.12 version will apply the model, and then override the texture (wooden sword) in the .json file with the spear texture. The 1.13 version replaces the model, but the texture override doesn't work, so the item remains looking like a wooden sword.
In previous versions of Optifine that supported CIT models, using "texture=" for an item using a custom generated style model would override the texture specified in the .json file. This doesn't seem to work in 1.13.1. The texture in the .json file will take priority instead.
Here are two example resource packs for comparison. (one for 1.12.x and one for 1.13.1) https://drive.google.com/open?id=13NaSx8foj1pRIcM_4UkWo2IcoCjl37Lx https://drive.google.com/open?id=16NrS4X4XUOiHwaB_ucbgPe-0ZOrcpCT3
Both resource packs will apply a custom texture and model to a diamond sword named "Diamond Spear". The 1.12 version will apply the model, and then override the texture (wooden sword) in the .json file with the spear texture. The 1.13 version replaces the model, but the texture override doesn't work, so the item remains looking like a wooden sword.