If you select the object and press [n] to bring up the ‘Transform Properties’ popup, you can press the little lock icon in front of the ‘Loc’ properties to lock the object’s ability to be moved on one or more axis.
hmm, should have read your post more carefully. Not sure for the case of particles.
I know about the linking,
that’s why I opened a new file, appended the birch_002 group, exploded the leaves dupliframes into separate leaves, joined those, added the low-res canopy and bascally reorganised the group, removing all parent-child relationships.
Turns out I cannot move the elements.
Outliner properties are selectable, transform properties are open.
[update]
Oddest thing.
I appended the objects of aforementioned file, now I can move them.
Probably something is still a bit iffy in the appending-linking setup.
When appending, the leaf material also gets lost.
Really, what is going on ?