Warning! I would backup your database before installing 2019 Fabrication CADmep (always a good idea anyways). Yesterday the download became available for us and after it was installed and Revit 2019 was opened it appeared to change some of our files in the database folder. All other users lost custom data information as well as the default units changed to metric and the GUID was missing.
The default units and missing GUID was not effected on my computer but all other computers pointing at the same database were effected.
We were able to roll the files in the Database folder back to fix the problem.