RTFM! You de-pressurize, and then you crimp the fuel lines as per manual! I did the same job a month or so ago, in my garage/workshop (I actually redid the entire rear unit, i.e. pump check valves, fuel line connecting the two pumps, accumulator, and fuel filter). Be ready to capture a tiny amount.

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)