Yes a little difficult to explain here, let´s see...
It could work in the opposite way:
1- You draw your walls
2- Place a symbol (bed, desk, chair, any symbol) this symbol has a record field for example Room type: Library.
3- When you hit Create Spaces from Walls, then the Custom Space Name displayed in the viewport will read that symbol record field (Library)
Cheers,
Juan
What you want is to define the space name in your symbol. The next step is to use the "create spaces from wall command". You want this command to use the name saved into the previous placed symbol as the name for the space object ?
This would only be possible by creating a custom script.
But I don't see the point honestly.
Since you take the time to put the space name into the symbol why not placing it in the space object itself ? It takes as much time to do either of those options, and imagine having 3 symbols with different names in a room, the script might not take the right one a result.
I believe you are better off naming the space objects manually unless I'm still not understanding your question.