Change log? I don't think there is one on a file by file basis. I simply trashed everything but the projects directory and reinstalled DBP, the editor patches 1.09 and 1.092, and patch 5.1.
As to triangluation, I think DBP/DirectX does that automatically anyway in 5.1. I have noticed that DBP returns a higher poly count using statistics than I see in my editor (which use quads and other mutli-sided polygons like hexes.) I don't think triangulation will alter the performance of your model beyond the fact that file sizes will increase.
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TAZ