You'll need to involve support to make the conversion.  There's a procedure that requires some specific commands to make the swap.

Let us know if that helps!

May be, but all the EMC peoples (support,...) do not say the same thing !

Some peoples say that the spare node must be "quick restarted", others say that this is not mandatory ?

I wish to know if a "change_nodetype" followed by an additional node install is sufficient to reintall the spare as a storage node.
I also wish to check that the only things to do to remove the spare node is to execute "nodedb delete if --addr=ADDRESS OF SPARE NODE".

Note : I am an EMC partner and I am trained to replace or to install new node.

You might be referring to a "kickstart" of the node - this is a process to reload a node with a particular function set (storage node, utility node, etc.).  For older versions of Avamar, the kickstart procedure was necessary, but I do not believe that is still true - you didn't mention an Avamar version in your message.

As an EMC partner, support should be able to provide you with the specific procedure for your version of Avamar and node configuration.

Exact, conversion works fine without kickstart for Avamar 7.0.2-47 :

= Spare has been removed with "nodedb delete node --node=0.spare.0"

= Spare was converted to storage node by means of change_nodetype

= And this node was installed as a new node after some update (Hostname,...)