Have you seen: https://www.harp.gl/docs/master/examples/codebrowser.html?src=src%2Fdatasource_custom-texture-tile.ts ?

You just need to implement the method:

function getTexture(tile: Tile): Promise<[THREE.Texture, CopyrightInfo[]]> {
        return Promise.all([new TextureLoader().load("resources/wests_textures/clover.png"), []]);
}

I.e. assuming you know the way in which your textures are cut, you just need to use the correct tiling scheme and you can add a custom data provider to the WebTileDataSource. Is that what you mean?