It doesn’t just replace the textures, it changes it to use a different set of textures on certain sides.
This is also not the only patch In the mod, just the first I grabbed.
Another patch example is for the Polished Slabs;
[
{
"file": "game:blocktypes/stone/polished/polishedrockslab.json",
"op": "replace",
"path": "/texturesByType",
"value": {
"*-up-free": {
horizontals: { base: "block/stone/polishedrockslab/{rock}" },
verticals: { base: "block/stone/polishedrock/{rock}" }
},
"*-down-free": {
horizontals: { base: "block/stone/polishedrockslab/{rock}" },
verticals: { base: "block/stone/polishedrock/{rock}" }
},
"*-north-free": {
"verticals": { base: "block/stone/polishedrockslab/{rock}" },
"east": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 },
"west": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 },
"north": { base: "block/stone/polishedrock/{rock}" },
"south": { base: "block/stone/polishedrock/{rock}" }
},
"*-south-free": {
"verticals": { base: "block/stone/polishedrockslab/{rock}" },
"east": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 },
"west": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 },
"north": { base: "block/stone/polishedrock/{rock}" },
"south": { base: "block/stone/polishedrock/{rock}" }
},
"*-east-free": {
"verticals": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 },
"east": { base: "block/stone/polishedrock/{rock}" },
"west": { base: "block/stone/polishedrock/{rock}" },
"north": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 },
"south": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 }
},
"*-west-free": {
"verticals": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 },
"east": { base: "block/stone/polishedrock/{rock}" },
"west": { base: "block/stone/polishedrock/{rock}" },
"north": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 },
"south": { base: "block/stone/polishedrockslab/{rock}", rotation: 90 }
}
}
}
]