You don't give an example of the actual text you're trying to replace so I wasn't sure if you were trying to replace the figure dash with an en dash or an em dash, so I tested both.
1. Replace a figure dash delimited by spaces with an en dash with spaces:
Queen Victoria throne-sat for six decades.
Queen Victoria throne - sat for six decades.
Queen Victoria throne- sat for six decades.
Queen Victoria throne -sat for six decades.
(replace: " - ")[ – ]
... produced the following correct output where only the second line was modified.
Queen Victoria throne-sat for six decades.
Queen Victoria throne – sat for six decades.
Queen Victoria throne- sat for six decades.
Queen Victoria throne -sat for six decades.
2. Replace a figure dash delimited by spaces with an em dash with spaces:
Queen Victoria throne-sat for six decades.
Queen Victoria throne - sat for six decades.
Queen Victoria throne- sat for six decades.
Queen Victoria throne -sat for six decades.
(replace: " - ")[ — ]
.. produced the following correct output where only the second line was modified.
Queen Victoria throne-sat for six decades.
Queen Victoria throne — sat for six decades.
Queen Victoria throne- sat for six decades.
Queen Victoria throne -sat for six decades.
note: I also ran the above tests using Harlowe v1.2.4 in case you were using it instead. and it also produced the correct output.