Hi, here's a super, simple conversion.
You may have done the same; gotten it right, and just didn't notice. The eye changes are very subtle.
But, you can verify it's loading by pretending to start a new, male character. Then going to hair "56" which is partially bald, and turn the character sideways using the arrows.
You should see that the eyebrows are no longer horizontal, but curved like the girls.
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In terms of general tips.
I'd really recommend unpacking the game files first. Then browse around the unpacked files to familiarize yourself a bit.
And, find, and download mods that seem similar to ideas you want to create.
Checking out other mods with similar goals can help point you in the right direction.
Resources:
Unpacking all the Game Files; so you can see the potential art, and data to be modded:
A simple one-way XNB unpacker for Stardew Valley. Contribute to Pathoschild/StardewXnbHack development by creating an account on GitHub.
github.com
General Modding Wiki:
Mods are packages of files which change Stardew Valley in some way. Mods can add features (like showing NPCs on the map), change game mechanics (like making fences decay more slowly), make cosmetic changes (like making your house look like a hobbit home), and much more.
stardewvalleywiki.com
Specific resources for creating Content Patcher mods; if you haven't seen it already:
Official ContentPatcher guide:
Mods for Stardew Valley using SMAPI. Contribute to Pathoschild/StardewMods development by creating an account on GitHub.
github.com
Wiki(Content Patcher section):
Creating Content Patcher packs
stardewvalleywiki.com
Json Validator(Helps check for formatting errors in the JSON files. Useful if your text editor doesn't support it.)