I'd do it this way:
- leave your existing installation running
- provision the station with default values
- start and verify it
- copy your old weewx.conf over the newly created one
- check your paths in your weewx.conf (WEWWX_ROOT, HTML_ROOT, SKIN_ROOT and so on)
- in case of using sqlite: copy your database to ~/weewx-data/archive, overwriting the newly created one, if the file names are the same, otherwise delete the newly created one, to have things tidy
- if any, copy all your bin/user files that didn't come with an installer to ~/weewx-data/bin/user/
- if your device isn't limited to exclusive access, run weewxd in the venv and validate
- if your device is limited to exclusive access, stop the old installation and run (the new) weewxd in the venv and validate
- once validated, enjoy
Depending on your hardware, you might want to copy the udev rules and apply them (~/weewx-data/util/udev)
Depending on your needs and environment, create and enable systemd scripts (~/weewx-data/util/systemd)