Same with me.

Step:

• sudo tcset tun0 --direction incoming --rate 10Mbps --src-network 10.8.0.6/32
• I want to change the rate from 10 -> 15Mbps
  sudo tcset tun0 --direction incoming --rate 15Mbps --src-network 10.8.0.6/32 --change
  but it got error (image above)
  [INFO] clipping specified bandwidth rate limit with the tun0 maximum bandwidth rate
  (15.0Mbps -> 10.0Mbps)

[ERROR] command execution failed
command=/sbin/tc qdisc add dev tun0 ingress
stderr=Error: Exclusivity flag on, cannot modify.

[ERROR] command execution failed
command=/sbin/tc qdisc change dev ifb7038 parent 1b7e:2 handle 243f: netem
stderr=Error: NLM_F_REPLACE needed to override.

Additional: With outgoing, the flag --change run sometimes it run success, sometime can't update.

Originally posted by @nobitran in #131 (comment)