You can do this with the functions in the "Boolean" palette, but not with other functions/VIs/Controls that have a boolean input. I don't know the innards of LabVIEW, but I imagine this kind of change has to be done on each function that needs to accept an error cluster and would be fairly difficult to implement on a global level. I could be wrong though
Because an error cluster is much more than a flag. It contains error code and message which are crucial for some functions to behave properly (example: many VIs of the Dialog & User Interface Palette). I can understand that it works with some boolean operations (but it is actually buggy, see this report) but I would not expect it to extend any further. Actually I wouldn't want it to.
No, the change does not have to be done on every function, David. It could have easily been done systemically.
The limitation was deliberate to minimize miswiring. It's way too easy to click the wrong terminal on a dense conpane, and in general we like the strong typing of LabVIEW. The Boolean palette was weakened because of the extreme utility of that palette.
Idea was explicitly considered & rejected by R&D - see Aristos Queue's post (above) for reasoning