X5R capacitor derating and highpass filters
"Derate" doesn't necessarily mean that the capacitance value changes -- it just means that some of the specs change.  For example, if the voltage rating for a 0.1 microfarad cap is 40V, derating by 75% would mean that you should not use it past 30V.

So, if you planned to use your high pass filter constructed with the above capacitor at above  30V, and it's spending most of it's time at DC, or with a large DC offset,  then yes, it is "affecting" the functionality of the circuit.