So I saw on Tumblr that GG would only have impersonated Graves for two days so it was definitely a crash in - crash out job. But sadly that interferes with my headcanon of Grindelwald trying very earnestly and not completely competently at being the Director of Magical Security enough to throw everyone off the scent.
Our cybergoth dark Lord in disguise trying to console that crying Auror who thinks they'll never last past the first month. Accidentally wandering into the women's lavatories. Hiding memos in potplants because he doesn't know to do with them. Having to go ask his captive what ORTF means and learning it means Obliviation Report To Follow while Graves is like, 'Really?'

I need Grindelwald as the I Have No Idea What I'm Doing dog basically.