I believe playing as someone else's character is powerplaying, not godmodding.
"Powerplaying" and "godmoding" - as I know I have explained before - are terms used interchangably depending on where you picked up roleplaying, and therefore the definitions mix here on tumblr.
Where I learned it, “godmoding” is controlling characters not your own, similarly to “playing God” on games like the Sims. Whereas “powerplaying” I learned as to mean having an overpowered and/or omnipotent character, which meant they were always one step ahead of all other characters. That could be in battle, where they are undefeatable, or in conversation, where they magically know what every other character is thinking, feeling, or has gone through without that other character saying it.
You can see how each phrase could fit to either definition, therefore it makes sense that the terms are a flip-flopped a lot. However, since that’s how I learned it, and this is my blog, those are the definitions I have attached to each phrase and is therefore how they are categorized on here. Though, you’ll notice, that since the terms are so similar, many older napkins with one of the two tags often has the other, as well.