I don't know how long it takes for fish to "forget" their territories, but one thing that helped me when my 6-line started becoming agressive towards my anthias was to spend a couple hours with the net, everytime the wrasse chased my anthias, he got the net swooshed at him to scare him into the rocks.
Did this repeatedly and after a couple hours the 6-line figured out not to bother my anthias. Make sure you wait till the fish actually commits the "offense" and just have the net ready hovering in the top of the tank.
Sounds strange, but it worked for me.
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