Better Artisan Good Icons - Content Packs
BAGI supports content packs to retexture custom items (or override BAGI's textures for vanilla items).

You can do this by creating a Content Pack. See https://stardewvalleywiki.com/Modding:Modder_Guide/APIs/Manifest for general info on how to create the manifest.json for a content pack.
For UniqueId you should use cat.betterartisangoodicons and for minimum version you should use 1.4.1.

Content Pack Format
BAGI expects a data.json file in the root level of the content pack (same level as the manifest.json). The format of this is as follows:

{
"Fruits": A list of fruit names you want to retexture or null if you don't want to retexture wine or juice,
"Vegetables": A list of vegetable names you want to retexture or null if you don't want to retexture pickles or juice,
"Flowers": A list of flower names you want to retexture or null if you don't want to retexture honey,
"Honey": A file path to a spritesheet containing honey images, or null if you don't want to retexture honey,
"Jelly": A file path to a spritesheet containing jelly images, or null if you don't want to retexture jelly,
"Juice": A file path to a spritesheet containing juice images, or null if you don't want to retexture juice,
"Pickles": A file path to a spritesheet containing pickle images, or null if you don't want to retexture pickles,
"Wine": A file path to a spritesheet containing wine images, or null if you don't want to retexture wine,
}

To retexture Wild Honey, use the name Wild. To retexture the base form of each artisan good (i.e. Honey/Wine/Juice/Pickles) use the name _Base in the Fruits/Vegetables/Flowers list.

The format of each spritesheet must be an image file, where each sprite is 16x16 pixels and occurs from left to right in the order of the list of names specified. You can have as many sprites in each row as you want, but don't make the spritesheet larger than it needs to be.

Example
For example, to just have Blueberry and Starfruit Wine retextured, the data.json would look like
{
"Fruits": [ "Blueberry", "Starfruit"],
"Vegetables": null,
"Flowers": null,
"Honey":null,
"Jelly":null,
"Juice":null,
"Pickles":null,
"Wine":"assets/wine.png"
}

and your content pack should have a folder named assets, which then has wine.png in it, which has a 16x16 image for blueberry wine either like
[Blueberry Starfruit] or
[Blueberry
 Starfruit].

More Examples
To see an example, look at assets folder in BAGI's folder. It loads the replacements for all vanilla sprites in the exact same way, so you can see how the images and data.json should look.

Also take a look at this mod: https://www.nexusmods.com/stardewvalley/mods/2925/ which provides sprites for some custom JSON Assets item for another example.