Can I freeze fresh hyssop?
In my experience, the answer for most leafy herbs is yes, fragance and flavor is preserved. Never tryed hyssop, however Gardening Know How site says it freezes fine:  


  it can be dried or frozen and stored for later use. When harvesting a hyssop plant, cut it in the morning hours once any dew has dried. Hang the plants upside down in small bunches to dry in a dark, well-ventilated area. Alternatively, you can place the leaves in a plastic bag after removing them from the stems and place in the freezer until ready to use.