It appears that the GSA is going to be doing more than just publishing a letter asserting that Joe Biden has won the 2020 election and therefore is allowed to access federal resources set aside to facilitate the transition. It's also going to fumigate and then sanitize the White House and other Executive branch office spaces prior to the Biden/Harris team, and their staff, occupying the building:
Here's how the GSA plans to disinfect the White House between Trump's departure and Biden's arrival
http://fin2me.com/politics/heres-how-the-gsa-plans-to-disinfect-the-white-house-between-trumps-departure-and-bidens-arrival/