Can the direction of electron flow in a voltaic cell be reversed?
Can going to non-standard conditions reverse the cell potential of a voltaic cell?


I have already answered that question, in the affirmative, for a simple tin and lead galvanic cell, here: https://chemistry.stackexchange.com/a/116734/79678.

What follows is an elaboration with some specific values and illustrative figures. In fig. 1, the tin and lead voltaic cell is shown:



In fig. 1, the tin and lead ion concentrations are each exactly $\pu{1 M}$ and the cell potential is $\pu{+0.014 V}$, with tin as the anode. All necessary equations are shown in the figure and the usual simplifying assumptions are made: unity activity coefficients, zero cell resistance, etc. The electron flow is from $\ce{Sn}$ to $\ce{Pb}$.

In the next figure, the lead ion concentration is $\pu{0.3363 M}$ while the tin ion concentration remains at exactly $\pu{1 M}$. This results in zero cell potential, as shown in fig. 2:



Since the cell potential is zero, it is a moot point to call tin the anode: the cell is not doing (net) electrochemistry. There is no net electron flow.

In the final figure, the lead ion concentration is exactly $\pu{0.1 M}$ while the tin ion concentration remains at exactly $\pu{1 M}$. This results in a cell potential of $\pu{+0.016 V}$, as shown in the figure: 



But now lead is the anode and tin is the cathode. The electron flow is from $\ce{Pb}$ to $\ce{Sn}$.

So changing the ion concentration to non-standard values can reverse the electron flow direction. But this was an especially easy case because the two metal electrodes had standard potentials that were relatively close. For the Daniell cell, with $\ce{Zn}$ and $\ce{Cu}$, it would not be feasible.