Actually, you can have your clones do exactly what you're describing.
The default behavior in Inkscape is for the clones to not move when the original is moved.
But if you go to the Edit > Preferences dialog (or Shift-Ctrl-P), in the Behavior > Clones section, the first item is "Moving Original".
There are three options:
Move in Parallel (which is the one you are wanting)
Stay unmoved (which is the default)
Move according to Transform (which can get really funky if there's a complex transform that's been applied to the clone. For example if you have rotated a clone, that will be in the transform (which can be seen in the XML editor) and the rotation will factor in to how the clone moves when you move the original.
Keep in mind that if you set the clones to move when the original does, that applies to all clones. So if you have clones of your clones, your clones are also "originals" for that next generation of clones, and those clones will move too, by whatever amount and manner is determined in your drawing. The results can be unexpected sometimes.
As far as your question about adding an extra object to your set of clones, it depends on what kind of adding you want to do. It's true that an object can only have one set of tiled clones, but there are easy options for different needs:
If you have tiled a 3x3 array of clones and decide you wanted a 4x3 set, simply change the Tiled Clones dialog to 4 rows, select your original, and then click the Remove button, then the Create button.
- As long as you have your original object selected, the Tiled Clones
dialog can remove them and recreate, along with any changes you make
to the settings.
- When you select the original, the Tiled Clones dialog will tell you
how many tiled clones it has (bottom left corner of dialog). This is
true no matter what other cloning or manipulations you've done since
you tiled it.
- Remember the original will be under the first tiled clone, so just
clicking on it will select the first clone, not the original. Two
easy ways to select the original are to Alt-click on the object
(which allows you to select objects under an object) or to select it
in the Objects dialog.
- If you've changed settings for tiling some other object in the
meantime, you'll need to change back to the settings you want for
this tiling. If you are tile-cloning many objects in a drawing, keep
track of your settings (on Shift tab, Color tab, etc.).
(Obviously, if you have some Randomizing set in the dialog, it will not repeat the exact placement when you Remove and Create again.)
On the other hand, if you are manually arranging the clones or just want an extra clone that you place where you want, just clone (not tile-clone) your original.
Just select the original and hit Alt-D (or Edit > Clone > Create Clone).
- You can do this as many times as you want, no limit, even if you have
already tile-cloned the object.
- Or you can clone one of your clones if you want.
- You can also Tile-clone one of your tiled clones you made. Or clone a tiled clone. Or tile-clone a clone. :-)