Change Block to Linked

I cannot manage to change an existing “Not linked” block which I have in my model in 10k instances.
Everything in the tab External is greyed out and exporting block definition to a file changes nothing… I remember exporting was a way to set the block as “linked” on Windows…

Is it even possible to exchange existing block for a different one in Rhino Mac?

Thank you for any tips

As far as I can see this is not working in Mac Rhino yet. In Windows you change this in BlockManager > select the block and choose Properties- there you can point a block at a file.