Right-click on a diagram label and choose Change To Constant. The plug-in will do a best-fit match to change the label into a constant of the best type it can find. It checks numerics first (except complex), then Boolean, then defaults to string. For Boolean, any capitalization of "TRUE" or "FALSE" or "T" or "F" will be converted.
Attachement is saved in LabVIEW 2015. For install instructions, go here.