Microangelo Librarian can remove specific image formats from one or more icons in an icon library.
Open the icon library with Microangelo Librarian.
Select Specific from Librarian's View menu.
Select the image format to delete using the Image Format control on Librarian's toolbar.
Select the icon(s) the current format will be deleted from.
Select Delete Format from Librarian's Edit menu.
Multiple icons can be selected for this action.
Depress the left button down outside of an icon and then drag to select a rectangular area within the workspace.
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Hold down the CTRL key while left clicking on an icon to add it or remove it from the current selection.