Sometimes toolbar buttons require 2 or 3 words to show what they are doing.
With a few of such buttons, they toolbar tends to become a bit too wide.
Suggestion: whilst looking at Explorer toolbar, maybe add 1 extra label?
It would indeed slightly increase the height of the toolbar.
It is a matter of taste of course, but personally .. I would prefer have the two lines.
Reason is that, even though there is a 'Tooltip', the label text still takes more space than desired.
Unless, of course, there is no label at all.
One may hoover over the buttons to see what it is doing, which is a bit slower then reading the label texts.
Often a description requires more words.
As for myself, the less frequently used on, I have added those to a kind of personal drop down menu in the toolbar already.
'/n' would also be nice.
This will require a slight GUI change then: a somewhat higher toolbar to make space for this 2nd line, probably about 5mm.
This 'small change', however, may mean a big overhaul from a programming point of view(?), I don't know.
Nonetheless it is still less then Windows Explorer.
Windows Explorer even reserves space for a 3rd line, as to show the category or drop down arrow or even 4 lines when replacing the icon with text.
Opus toolbars already support dynamic sizing if needed to display labels. In fact your toolbar is using it. Switch the label state for your entire bar to right and it's width will decrease. This is best illustrated with a vertical toolbar:
As you can see, OPUS toolbars can autosize to fix massive labels.
For your idea to work it would really just be a matter of implementing a way for the user to define max width. Thinking over my previous suggestion of having a /n character, I think something like that could get tedious if you have a lot of items exceeding 1 line.
The best solution would be to just add an additional option at the toolbar level that specifies label line length.