If you measure the O.D. of cells at one wavelength, is it possible to find its equivalent O.D. at another wavelength?
O.D. can mean 30 different things, many of them being related to science and to optics (see here)! I'll assume you mean absorbance (for Optical Density I'd guess) or light scattering as @canadianer said

Each substance has its own absorption spectrum and reflectance spectrum. Knowing only the absorption is a given wavelength does not tell much about the absorption at another wavelength (at least not without some other a priori knowledge about the substance studied).

So, the answer is 'no'.