If you just scale parts, it will reduce the wall thickness leading to part more difficult to print and too fragile.
If I find 10 min, I will try to modify the current Solidworks parts (no-scaling) with similar dimensions as should be a Poppy Humanoid mini.
Maybe a design from scratch would be easier, to do so, @jgrizou has built a OpenSCAD library to create part for XL320. The ErgoJr is done with that techno for example.