Question

Is capacitance constant in a capacitor? I'm thinking yes?

Answer 1

C=Q/V and Q=It , hence with a change in the current, I, and with a change in the voltage, V, the capacitance may change.
The definition of capacitance is 'the ability of a body to hold an electrical charge'.. when we say that this capacitor has a capacitance of 10mF, we mean that its maximum ability is 10mF, but it can go below that depending on the Q and V.

Answer 2

look at the "american journal of physics" by camillo cuvaj about capacitor