Slow pulsed capillary discharges are under investigation for use as plasma channel waveguides in laser-wakefield acceleration and high-harmonics generation. The channel radius has a strong influence on the plasma and guiding properties. Hence, it is expected that the guiding properties can be manipulated by locally modifying the radius. This presumption has been investigated by means of a numerical simulation of a channel with a periodically modulated radius. The simulation revealed a strongly nonlinear response of the plasma and wall properties to the modulation. However, no modulation of the laser guiding properties is observed.