Silver wire, the basic stuff even (2N/3N) has lower resistance than 6N copper … and that’s definitely measurable.
We’re talking very small resistances to begin with, however. Low enough that you cannot reliably measure them with a standard multi-meter and either need a specialty instrument (a dedicated low-ohm meter) and/or special techniques.
To give you an example, a 1000 ft run of 6N copper wire at 24 gauge would have a resistance of about 25.5 Ω. In comparison, the same run in silver would be about 23 Ω. Of course if you increase the gauge of the copper wire to, say, 22 gauge, then its resistance for the same run would drop to about 16 Ω. And adding more runs of wire, drops it further (larger effective gauge).
Now, if you mean are there measurable differences in the frequency response of a copper vs. silver cable, when simply measuring the cable itself? Not at audio frequencies. And even up around 200 kHz, the differences are measured in small fractions of a dB (you’d have to hit at least 0.5 dB, in the most sensitive range of hearing, to have any chance of that being audible). Though the higher you go, the more severe they become.
It is worth noting that when dealing with dynamic transducers (i.e. something with a coil that acts as an inductor) then the impedance and the capacitance of the overall circuit can result in effects that interact with the coil that can affect response. In fact, this is done deliberately in crossovers to help mitigate the reactivity of the voice coil and keep response constant.
But the resistance and capacitance present in any normal cable are far too low to have any useful effect in this regard with normal headphone transducers.
You could specifically build such a thing into the cable, though it would only work properly for a specific driver/coil, but you’d need an actual capacitor and resistor to do it as the values present from the cable itself are far too small.
There are good reasons to buy some types of cable in the audio world. Special geometries, shielding and noise-rejection if you need it (electrically noisy environments, long cable runs). Appropriate gauge cabling when dealing with power (speaker and mains cables) and/or long cable runs.
And then there are both ergonomic and aesthetic concerns … i.e. cables that offer more flexibility or less mechanical noise/microphonics (anyone that’s used the stock Focal cables on the Elegia, Clear and Stellia are well aware of these two), length, design/aesthetics.