How can I add my Argon to an existing Particle network?

[ScruffR]

What is a Particle network?
If you mean an existing mesh, then yes, you can via CLI (see particle mesh --help).
But, while the idea was that any gateway capable device which joins a micro network that doesn't currently have a gateway assigned to it would be promoted to become the new gateway automatically. As it turns out that feature doesn't (currently) work as intended.
See this thread

I mistakenly deleted my argon (Mesh with 17xenon)

Hi Katala, A bit of an update on this. I spoke with our engineering team and it’s my understanding that if there are no available mesh gateways on the network, the network should try to promote any available gateways on the network. I’ve personally not tested this configuration much, but do recommend you give it a shot and share the results here with us. You should be able to re-add your Argon to the existing mesh network through following these Mesh over USB setup instructions for adding a No…

@pierrep

Given the 10 network limit stated by Particle, I’m keen to re-use the existing one.

That limit only means 10 concurrent, current networks. Once you remove all devices from an existing network the network will disappear and your 10-network-quota will get that one now free instance back.