How to assign reference to a variable on clients

My game is played with maximum 4 players. Each can instantiate(spawn) object with authority. They do it through a Command invoke.

So I call Command, and on the server the object is instantiated and spawned with authority.
After that step, I want to have reference to that instantiated object on the GamePlayer object with a new script. I can set it now but only with a ClientRPC call and there must be at least two GameObject parameters.
One is the GamePlayer object that I want to access to it's script and set this script's variable, the other parameter is the GameObject reference of newly instantiated/spawned object.

Is there an easier way to do it?
Does it cost too much to send GameObject references with Command and ClientRPC calls. Also

I realized I can't put Custom C# class parameters in those command and clientrpc functions, and also can't make those custom monobehaviour variables as SyncVar.

Is what I do bad for optimization? Should I proceed with this method of implementation.

 

Second question;

I need to get MatchInfoSnapshot instance of newly created match. I can get it when joining as a client but docs are not saying how to get it after creating the match.

I need this because I want to set a seed integer from the match name string for all players, to create a procedural terrain same for all players.

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I'll workaround it with this way if anyone needs something like this, inside OnMatchCreate callback, I listed all matches again with the created match's name as a filter. And then in a foreach loop, I checked if the created game's network id and the snapshots network id is the same or not, if it's the same, I use that snapshot.