TOPPView also offers editing functionality for feature layers.

After enabling the feature editing mode in the context menu of the feature layer, the following actions can be performed:

Features can be dragged with the mouse in order to change the m/z and RT position.
The position, intensity and charge of a feature can be edited by double-clicking a feature.
Features can be created by double-clicking the layer background.
Features can be removed by selecting them and pressing the DEL key.