Can taking bovine colostrum increase plasma immunoglobulin levels, thereby masking an underlying immunoglobulin deficiency by altering blood tests?

Unlikely: Very thoughtful idea. Unfortunately, the bovine immunoglobins are too large to be absorbed from the intestine and would be digested by stomach and intestinal juices and enzymes. With use you would be providing body with raw materials for making your own immunoglobulins, but at a cost. Any "complete" proteins from eggs or milk could provide the same protein precursors and support good health.

Unlikely: Most of the antibodies present would be destroyed through digestion and enzymes in the GI tract.