You do not need to retune.
This is what I did, install the BPV. Remove the cap on the side to vent to atmosphere.
hook everything back up, start the car. See how much your piston opens, I adjusted mine so the piston was fully opened at idle.
turn the car off, discount your battery, install the cap on the side. hook your battery up after 15 mins, and it should be good to go!
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