Trying to accurately simulate LED lighting and a lense

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What file format could I use so that keyshot could treat the part as one material, but allow me to put different texture on different parts?

Not knowing Alias at all, you can certianly just run the gamut of tests on all the possible export options, starting with the obvious ones, obj, FBX, stl, stp, etc, and see if it gets you where you need to be. Keep in mind that KS has a Geometry Editor that will allow you to split apart surfaces and/or objects. So, if for example  you are able to get the lens to import as one piece, but want to split the top surface from the back, you can do that operation inside keyshot easily. This is good for the times when you need to do this to just one or two objects. I deal with CAD files mostly and I use this quite a bit, where the plastic injection is all made from one cad piece but the actial mold has different textures that is imparts to a single piece. I get the whole mold cad, then I split off the smooth faces for labels, and leave the textured pieces as one piece.

I tried this, but it came out really weird.  It was like Keyshot was not treating the object as solid anymore; instead it was the A side (textured but no thickness at all) and the b side (smooth, no thickness at all).  It was like the interior of the part did not exist, so the optics got super weird.