That's what the VRA says. Any confirmed official from anywhere in the government or any GS-15 (or person paid at least as much as a GS-15) from that department. It's how Trump put Mulvaney temporarily in charge of the CFPB, altho technically he's been in charge there longer than the 210 day limit.
Yeah, I've been through the VRA a whole bunch since all this stuff is happening, so I know that's how it's worded. But I wonder if that confirms to the constitutional intent of senate confirmation, that it's a free pass to act in ANY senate confirmed position.
And I happen to know why Mulvaney is in place past 210 days! Kathleen Kraninger was nominated to head CFPB 7 days before his 210 days would have been up, and VRA specifies that the person in the acting position can continue to do so while there is a nominee in place. If the nominee is rejected or withdrawn, the acting person can go for
another 210 days. Then there can be another nominee, then
another 210 days. Kraninger was nominated on 6/16/2018, 158 days ago, meaning Mulvaney has been there for 361 days. If Kraninger is withdrawn or defeated, Mulvaney gets to reset the clock.