How do I select points of multiple objects for modification?

[toolforger]

I have a floor plan with an unknown number of rectangles - probably dozens, maybe hundreds.
(There are more types of objects, but they do not matter, as I know how to keep them out of harm’s way. Let’s pretend it’s only rectangles.)

There is a mistake in that floor plan: One vertical distance is too small.
I.e.

• I have a horizontal line.
• All objects below that line must move down.
• All objects that straddle that line must have their height increases.
  Imagine cutting the drawing at the horizontal line, inserting a paper strip, and reconnecting all the cut-up rectangles.

The approach that I know from a CAD program I had access to earlier was:

1. Activate point selection mode.
2. Do a rectangular selection of the entire drawing below the line. The points would be from multiple objects.
3. Move the selected points down by whatever amount I wanted.

I Draw, I cannot find a way to select points from multiple objects; is that indeed the case?

The alternative approach that I can come up with is:
Select all objects that are completely below the horizontal line, move these down by the needed amount.
Select all objects that are partly above and partly below, then increase their height by a given numeric value. (Is such an operation even available? I have no idea how one would name it, so I can’t find it. It’s NOT scaling: Scaling vertically would move each point down by a different amount depending on its exact y value, I need something more binary, something that leaves all points above the line unmodified and moves all points below it by the intended distance.)

[EarnestAl]

@toolforger

Select all objects that are completely below the horizontal line, move these down by the needed amount.

1. Drag a selection rectangle around the lower objects. Only the objects completely included will be selected. If anything unwanted is included in the selection, Shift+Click it to deselect.
2. Click Format > Position and size (F4 possibly Fn+F4) and select the Position and Size tab
   1. In Position Y add the existing position value to the amount you want to move and enter that number in the field
   2. Position Y is the top left corner of the selection so make sure that the dot in the Base Point is also set to the top right. It will be by default but it is worth getting into the habit of checking that you are adjusting the point you want.
   3. Click OK

@toolforger

Select all objects that are partly above and partly below, then increase their height by a given numeric value.

1. Drag a selection rectangle around the upper objects. Deselect any unwanted inclusions
2. Click Format > Position and size (F4) and select the Position and Size tab. Under Size:
   1. Untick the box next to the padlock (tooltip Keep ratio)
   2. In the Base point diagram, select a point on the upper row (we are changing only the height)
      I presume that you want to increase the height of the objects by keeping the top the same but extend downwards by the same amount you moved the lower objects down
3. In the Height field enter the sum of the existing value and the amount by which you wish to increase the height
4. Click OK

@toolforger

The approach that I know from a CAD program I had access to earlier

There is an extension to add some CAD operations to Draw, CADLO » Libreoffice Extensions

[Edit]
For the above operations, make sure that Point Edit Mode is off (unhighlighted), Edit > Toggle Point Edit Mode (F8)