Good view of FTS explosives being installed and note he says they must be added before stacking.
Video will start at 8:01
https://youtu.be/v4cQDa8oilQ?t=481
We seem to be focusing on different things. There are two steps.
One: you load the primer caps and boosters (the initiating explosives). The system is now primed.
Two: you pull the flight pins and insert arming plugs completing the firing circuits. The system is now armed.
Step one is done as a final assembly of a ship for an actual launch.
Step two is done exterior to a fully assembled ship and happens only hours before launch.
Step one would be omitted in any case other than launch; this has been my primary point of news.
Step two is always done very last and does not require anything other than a person on the outside of the rocket to pull pins and insert arming plugs into the empty sockets. This is very much by intention.