When selecting "Leads To", do not include the systems already selected for auto-filling "Leads To" in that system.

[Bluedagger21]

If someone really wants to switch the connection, they should just remove the connection from the other first, then select it in the other Leads To.

[Bluedagger21]

Bumping this enhancement request some as it would be a big QoL time-saver for adding these connections.

[exodus4d]

Already linked systems got moved into a separat group and are no longer available for select until they get un-linked from its signature.
Auto-pre-selection is not implemented for now. This might become complex to implement. Maybe in future...