There is no so-called "extra point charge" in this context. Electron density is calculated directly based on wavefunction according to the equation given in Section 2.6 of Multiwfn manual.

I would like to plot the electron density along a line. To achieve this, I would simply do the following after loading my file into multiwfn:
3
1
2
-5,0,0,5,0,0 A
However, I guess the default for the extra point charge used to compute the ESP is q = -1.00. Is there a way to tune this value, so that one could compute the electron density along a line with different values of q?

Thank you