Renaming
Once an explicit button has been created, its label text must be treated specially. Any inter-word spacing within the label may be freely changed, as may happen when a paragraph is refilled, but a special command must be invoked to rename it.
The rename command operates in two different ways. If point is within a button label when it is invoked, it will tell you to edit the button label and then to invoke the rename command again after the edit. The second invocation will actually rename the button. If instead the command is originally invoked outside of any explicit button, it will prompt for the button label to replace and the label to replace it with and then will perform the renaming. All occurrences of the same button in the buffer will be renamed.
The rename command may be invoked from the Hyperbole menu via Ebut/Rename. Hyperbole does not bind this command to a key by default. {C-h w hui:ebut-rename RET} will show what if any key is bound within your Emacs. Bind it within your ~/.emacs file with: (hkey-set-key "\C-cr" 'hui:ebut-rename), for example.