Increasing, decreasing netmask with iproute2

Hello everyone

I am playing with changing netmask for ip v4 address and find out that
there is no
other possibility to do it except:

ip address add 1.2.3.4/21 dev <device>
ip address del 1.2.3.4/24 dev <device>

Looks like all is working but I would like to get official answer
that this is safe to do in such way?

Look forward to your answer.
Thanks in advance.