Yes, increasing the capacitance will lower the resonant frequency, which is equal to 1 / (2 * PI * square root (inductance * capacitance))

Four times the capacitance will cut the resonant frequency in half. Insert lots of hand waving here for not taking into account stray capacitance and inductance, how the loop is wound, diameter of the wire, phase of the Moon, and the square root of the distance to Chuck Norris.

There's practical limits to how much you can lower the resonant frequency by adding more capacitance, and I defer to any advice from jFarley when loop antennas are concerned.

Another thing you can do of course is to go with more than one turn on your loop, if you want to lower the resonance frequency but keep the overall dimensions reasonable.