Trimming vent feathers is very normal especially for english budgies during breeding season.
You don't even have to trim them. Budgies can reach their vents with their beaks. This is how we end up with poop sticking to the walls
Because they flick the poop around when it gets stuck to their vents while getting rid of them.
From time to time, Mika has poop stuck around her vent and she manages to get rid of them. As long as it is not blocking the vent itself, it is not a problem