On my Proxmox server the configuration is permanent. Non need to reapply each time.
I just checked, as you can see below:
[Unit]
# network-online is really needed, otherwise there are problems with snmp
# -> 865620
After=network-online.target
Description=UPS power management daemon
Documentation=man:apcupsd(8)
[Service]
RestartSec=30
ExecStartPre=/lib/apcupsd/prestart
ExecStart=/sbin/apcupsd
Type=forking
KillMode=process
PIDFile=/var/run/apcupsd.pid
[Install]
WantedBy=multi-user.target