..enter the whole wall, then erase parts?

Not to my knowledge - unless you insert an invisible window/door (must be placed/resized without magnetism - ALT key - if wall is curved - see thread 5366 ). But it is probably easier to edit wall elements manually with wall properties (start- and endpoints + arc extent).

Maybe you could use your existing plan as background image (select walls in the 2D window, copy, paste into a graphics editor, save as png and import as background image). If you draw on top of the background image, maybe it is easier?

Just a thought, but hard to tell without knowing more about your design. ok