Cool question.   The answer is chemistry.   If you happen to know the amino acid sequence of a specific biopolymer, excellent [even if someone else did that already]!

You know then the most abundant amino acids and the mole ratios,  so if there is an Asp and Glu site, one could make an ester with only those sites.  If one knows the amount of  Ser, one knows the amount of OH sites to which one could do a chemical reaction.

The results will not be perfectly stoichiometric because some molecular binding sites could be hidden from the surface.    The thing is one can never do BETTER than the reacting with a fraction of the total starting number of chemically correct binding sites.

It is true that physically modifying the surface of a biopolymer could expose more sites than had been present initially.  However, that would be a rather useless experiment unless one has a way of measuring the degree of disruption of the surface. 

Need to have at least one solid mechanism that locks in knowing that a particular treatment modified  X, Y, or Z property resulted in  X2, Y2, or Z2 effect.

Walter

Thanks Schmidt, your answer is impressively explanatory and absolutely helpful.