Requirements
Automatron DLC

User guide
Install mod.
Load game.
Trade with Codsworth and take the "CodsworthController" holotape
Use it in your pipboy.

How it works
The all-in-one-button is very easy to use and works in three stages where the previous ones must have been passed for any following to appear.
1. Is Codsworth more than 500 units away? If so move to player position.
2. Is he in a power armor frame? Eject him.
3. If he's close and out of any frame? Toggle the race change.

When changing race Codsworth combatstyle is set to Hancocks meaning any mods that edit/improves his way of fighting should affect Codsworth too.
He is also given the Settlery-type infinite ammo and Danse indestructible power armor functionality.

Finally, if you're using my Wintermute mod you can also make more extensive customizations using its Master Control Program as long as you don't change the voice since it's Codsworth specific. This functionality is activated by issuing a "addkeyword WintermuteCyborg" in console with Codsworth targeted and then selecting him as usual with the control rod.

Known issues
Cannot modify human form with automatron mods - Yeah that breaks a lot of things so don't expect to give Codsworth a lasergun hand Cobra style. Installed mods that give the player bonuses like regeneration or damage resistance might still work though, let me know.
Animation issues - Sometimes the animations get frozen, particularly if you toggle mid-movement, but you can reset them by putting Codsworth in the robot workbench again and hover the mouse over the different options for the affected body part to fix it. Traveling, putting Codsworth in power armor or any other action that applies/resets animations should also fix it.
Refusal to fight - If you toggle between robot and human form either can end up with the wrong weapon equipped. Make sure you unequip any human weapon before changing. If you forget this just change back to human form and unequip the weapon. If you're using automatron weapon mods you might need to remove and reattach them in the workbench too to make sure both the correct robot weapon and ammunition is equipped.

Disclaimer
This mod hasn't been tested in a full or even partial playthrough and neither in a vanilla otherwise unmodded game. I had it as a running side project while working other stuff mostly sandbox type play. I reached full affinity and obtained Codsworth's perk without problems though.
However, I wouldn't recommend using this mod if you want to make sure Codsworth is 100% functional by keeping him as the "game intended". If you already got his perk or otherwise can afford him going where no Mr Handy has gone before and never coming back, then it might be a better idea.