Is it possible to toggle ÜberCharge visual effects?

Solution 1:

I still don't know exactly why you want to do this, but just to attempt to clear this up:

You can use the console command addcond 5 to Über yourself. You can use the command removecond 5 to unÜber yourself. These are both cheats commands, so they require sv_cheats to be 1 on the server side.

There is no command to enable or disable only the visual effects. As far as I am aware it is impossible to create a client-side mod that allows you to see the effects when not Übered, as this would require hijacking the rendering code that checks to see whether you are Übered, which seems like it would require ridiculous reverse-engineering and probably might trip VAC.

Solution 2:

Client-side? Yes. Server-side? No.

When communicating with another person over a server that is not your own, there is no conceivable method of changing the effects for anybody but you, unless said person performs the same steps as you do. However, even altering the effects is considered tampering with the game, which could, and most likely will, result in a VAC ban.