The lines don't usually just "pull out". They will require some effort. On most there is a slight flare on the end of the line just beyond the rubber sleeve. The sleeve gets expanded into the opening in the pump or filter base when the fitting is tightened. and won't simply slide out. When I need to remove one I expect to replace the sleeve because it usually comes out in pieces. Thye become brittle with age and often require being broken up with a sharp pick for removal. As for checking the fuel flow, you should be able to flush the lines well enough without removing them by turning the fuel on with filter removed and operating the supply pump. This should cover all but the final stage from filter to injector pump, which should not be an issue anyway if the filter did it's job.
