How to modify the alert manager's threshold value

I use a node exporter program to monitor the CPU's threshold and receive notifications. The example below is a rule file that sets conditions when it is more than 80%.

alert: HostHighCpuLoad
expr: 100 - (avg by(instance) (rate(node_cpu_seconds_total{mode="idle"}[2m])) * 100) > 80
for: 0m
labels:
  severity: warning
annotations:
  summary: Host high CPU load (instance {{ $labels.instance }})
  description: "CPU load is > 80%\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}" 

I need to receive a threshold from the web UI and change the threshold set in the rule file to 70%. Can I convert the threshold into a variable?

expr: 100 - (avg by(instance) (rate(node_cpu_seconds_total{mode="idle"}[2m])) * 100) > {THRESHOLD_VALUE} 

Or I wonder if I should make a script that modifies the 80% value to 70%. Please give me advice.