Weak interaction and charge conjugation $C$ Does the weak interaction always change the charge of all participating particles?
And in this context, what does $C$-violation do then?
 A: The always charge-conserving weak interaction most often changes species of particles; it doesn't  change their charge. 
Consider the iconic charged current weak reaction, 
$$
  \to e_L ~\bar \nu_{eR} ~\nu_{\mu L} ~, 
$$
while the C-symmetric reaction with the same chiralities is not the actual decay that goes,
$$
 \bar \mu \to e^+_R ~\nu_{eL} ~\bar \nu_{\mu R} ~. 
$$
So the weak interaction violates C maximally, since the first reaction has a left-chiral electron,  whereas the second reaction  has the positron be right handed. So the second reaction that actually goes requires a P operation to be applied at the same time to yield the C-conjugate of the first one. Then CP  is (mostly) conserved, while both C and P are violated maximally. 
So C and P are not  good symmetries of these weak decays, but CP mostly is.
A: Weak interaction vertices involving a charged $W^+$ or $W^-$ boson change the charge of the quark or lepton by $\pm 1$. Weak interaction vertices involving a neutral $Z$ boson do not change the charge. The point is that charge is conserved, but not all of the weak bosons carry charge.
