How to make unitlines.json work?

There is a unitlines.json in the dat folder to define unit-lines.

I made a DATA mod contains many new units, so I have to modify this json.

But I found it doesn’t work if I put the json in the DATA mod. And if I put it in a UI mod, the mod turns into a DATA mod because there is a file in the dat folder.

So how can I make the unitlines.json work?