ご質問の程ありがとうございます。
Catalyst 9300の電源を付けた状態で、SSDを挿入することは可能になります。
ご参考までに、電源を付けてSSDを挿入した場合、下記の様なログが出力されます。
SW1#
*Jul 10 01:52:51.691: %IOSD_INFRA-6-IFS_DEVICE_OIR: Device usbflash1 added.
*Jul 10 01:52:51.676: %IOSXE-0-PLATFORM: Switch 1 R0/0: udev: usb1: has been inserted
SW1#more ?
/ascii Display binary files in ascii
/binary Force display to hex/text format
/compressed Force display to compressed format
/ebcdic Display binary files in ebcdic
/error Allow error files to be displayed
bootflash: File to display
cns: File to display
crashinfo: File to display
flash: File to display
ftp: File to display
http: File to display
https: File to display
null: File to display
nvram: File to display
rcp: File to display
scp: File to display
sftp: File to display
system: File to display
tar: File to display
tftp: File to display
tmpsys: File to display
usbflash1: File to display
webui: File to display