My full question is
"A total charge $Q$ is uniformly distributed within a spherical shell with negligible thickness compared to its radius. A point charge $q$ ($q<< Q$) is taken away from the shell's north pole and replaced on its south pole without affecting the rest of the charge distribution. What is the electric field at the centre of the shell?"
I don't really know how to apply symmetry to this, in a normal uniformly charged shell the field inside would be zero, but for this..? Would using Gauss's law with non-uniform charge distribution be appropriate at all (even though no charge is enclosed at the centre)? Shall I treat the poles like point charges of 0 and +2q, is there some type of superposition thing I'm missing?
This has really stumped me.