Dear Max Emmanuel 

Please, refine and reformulate you idea to get good responses. Generally, the conductivity of any material can be increased by its doping using any dopant material but cannot be injected by electrons. The resistance or the conductivity is a define property of each material  

Best regards

Dear Emmanuel

You can increase the conductivity of the material by increasing the number of free electrons by doping with suitable impurity in semiconductors in extrinsic range but not by charging a material.

Dear Mr. Emmanuel,

It seems almost impossible to change the electrical conductivity of a material by injecting charge into it. Electrical conductivity of a material is an intrinsic property of the material which depends upon the available structural positions for electrons. So if you wish to change the electrical conductivity of the material then you have to create such interstitial positions instead of deploying charge there. Every system tends to remain in a state of least potential energy. Anyhow if we could inject charge into it, without creating postions for the charge to accomodate into it, it will drain out rapidly as soon as the sample will be connected to an external circuit. This will give a momentarilly high current but this will not mean that the conductivity of the sample is increased. Thus if you wish to change the electrical conductivity of the material you have to create some of the extra interstitial sites to accomodate extra electrons and this may change the electrical conductivity of the sample.

With best regards,

Suresh Sharma 

What will happen with extra charges added to the sample?  They will be distributed at its surface, thanks to Coulomb repulsive interactions.  The second part of Suresh Sharma's answer comes next, so I don't repeat it.

If not convinced, think about an empty box into which you inject electrons.  The conductivity of initial vacuum remains unchanged.