Why does `ip route replace` add a duplicate new route?

Question

These are my ip routes,

default via 172.16.42.1 dev ens5 proto dhcp src 172.16.42.248 metric 100 
default via 172.16.42.1 dev ens3 proto dhcp src 172.16.42.79 metric 100 
default via 10.2.64.1 dev ens4 proto dhcp src 10.2.69.64 metric 100

I used ip route replace with the intent to lower the metric and raise the priority, like this,

sudo ip route replace default via 10.2.64.1 dev ens4 metric 90

However, this didn't replace the route, it added to it, now I've got,

default via 10.2.64.1 dev ens4 metric 90 
default via 172.16.42.1 dev ens5 proto dhcp src 172.16.42.248 metric 100 
default via 172.16.42.1 dev ens3 proto dhcp src 172.16.42.79 metric 100 
default via 10.2.64.1 dev ens4 proto dhcp src 10.2.69.64 metric 100

Is there anyway to change the metric on this line,

default via 10.2.64.1 dev ens4 proto dhcp src 10.2.69.64 metric 100

Without adding a new route?

Answer 1

The answer is that you can't, for reasons found here

Currently you have delete first, and then add.

sudo ip route del 10.2.64.1 via 30.1.2.2
sudo ip route replace default via 10.2.64.1 dev ens4 metric 90