  Flavor symmetry and symmetry breaking, K^0-\bar{K}^0 mixing and possible
effects of new physics on CP violation in weak decay modes D^{\pm} \to K_{S,L}
+ X^{\pm}, (K_{S,L} + \pi^0)_{K^*} + X^{\pm} (for X =\pi, \rho, a_1) and
D^{\pm}_s \to K_{S,L} + X^{\pm}_s, (K_{S,L} +\pi^0)_{K^*} + X^{\pm}_s (for X_s
= K, K^*) are analyzed. Relations between D^{\pm} and D^{\pm}_s decay branching
ratios are obtained from the d \Leftrightarrow s subgroup of SU(3) and dominant
symmetry-breaking mechanisms are investigated. A CP asymmetry of magnitude
3.3\times 10^{-3} is shown to result in the standard model from K^0-\bar{K}^0
mixing in the final-state. New physics affecting the doubly Cabibbo-suppressed
channels might either cancel this asymmetry or enhance it up to the percent
level. A comparison between the CP asymmetries in D^{\pm}_{(s)} \to K_{S}
X^{\pm}_{(s)} and D^{\pm}_{(s)} \to K_L X^{\pm}_{(s)} can pin down effects of
new physics.
