[R&F] How to copy builder as unique unit?

[iieeann]

Hi, I am thinking of making builder as unique unit for a civilization, but seems the same way of copying other unique units can't be applied to builder (tried with settler & military engineer also failed). I missed Civ4 India fast worker...

What could be the limitation? The game not only not loaded with new unit but simply just crashed

 

[isau]

I'm pretty sure there's a mod out there that does copy the Builder unit. It may be a mod involving slavery/a slave unit if I remember right.