  We present a photometric and structural analysis of 42 E/S0 galaxies in (E/S0
+ S) pairs observed in the BVRI color bands. We empirically determine the
effects of interactions on their morphology, structure and stellar populations
as seen from the light concentration (C), asymmetry (A), and clumpiness (S)
parameters. We further compare these values to a control sample of 67 mostly
isolated, non-interacting E/S0 galaxies. The paired E/S0 galaxies occupy a more
scattered loci in CAS space than non-interacting E/S0's, and the structural
effects of interactions on E/S0's are minor, in contrast to disk galaxies
involved in interactions. This suggests that observational methods for
recognizing interactions at high z, such the CAS methodology, would hardly
detect E/S0's involved in interactions (related to early phases of the so
called `dry-mergers'). We however find statistical differences in A when
comparing isolated and interacting E/S0s. In the mean, paired E/S0 galaxies
have A values 2.96+-0.72 times larger than the ones of non-interacting E/S0's.
For the subset of presumably strongly interacting E/S0's, A and S can be
several times larger than the typical values of the isolated E/S0's. We show
that the asymmetries are consistent with several internal and external
morphological distortions. We conclude that the interacting E/S0s in pairs
should be dense, gas poor galaxies in systems spaning a wide range of
interaction stages, with typical merging timescales >~ 0.1-0.5 Gyr. We use the
observed phenomenology of these galaxies to predict the approximate loci of
`dry pre-mergers' in the CAS space.(Abridged)
