How do I change the name of the cellular network operator?

You get a SIM from from some other provider and change your service to them.

I don't know the market in Russia to know the process for porting your service from MTS to someone else, but the label that appears on screen comes from your cell phone provider, so changing the label means you need to change provider, too.

That is broadcasted by your cell carrier, you can't change it.

That string is selected by your carrier. Change your carrier. Or petition your carrier to change the string they are using.