Multi-PSK on Hostapd

[Colton Conor]

I am trying to figure out the proper way to have multiple PSKs on a
single SSID. Each passphrase will be used by multiple users, and each
passphrase will be tied to a VLAN.

Reading https://w1.fi/cgit/hostap/tree/hostapd/hostapd.wpa_psk, it
seems the proper way to do this would be:

vlanid=10 00:00:00:00:00:00 passphrase1
vlanid=11 00:00:00:00:00:00 passphrase2

My question is:
What is the keyid= used for typically?
Is there a way to add/remove keys using radius instead of manually
editing the hostapd.wpa_psk each time?
Does editing the hostapd.wpa_psk kick existing users offline if you
have to reload / save the file?
How would you automate this across 100's of APs at a property?