I see. So in essence you agree, that syncing etc. is fully possible, but you just do not like the standard way, but want to use a different way

Agree...
First a bit of info:
The 'Additional' script, media and cartwall libs are kept in a special config file called "ProppFrexx ONAIR.scriptlibs", "ProppFrexx ONAIR.cartwalllibs" resp. "ProppFrexx ONAIR.medialibs".
These file by default are located in your config folder.
The mixing settings ("ProppFrexx ONAIR.mixing") are equally located.
When e.g. adding new scripts, they are registered within these files (e.g. "ProppFrexx ONAIR.scriptlibs").
So you need to ensure, that the above mentioned files are located on a shared config folder.
And that they are used by all shared ProppFrexx instances.
So that when you make changes within one instance...they are accessible by another instance in the same way.
Note, that you still need to reload them (on instance A) when you made a change (on instance B) - but see the above mentioned automatic reload in case of RemoteClients!
Anyhow, there is a global option to use to define a global/shared location for all the above config files!
Yyou might use the "-globalconfig" command-line option when starting ProppFrexx ONAIR:
-globalconfig <path>
Defines the location (relative to the executable location or absolute path) to certain global configuration files. Namely:
• Additional Media Libraries (file ProppFrexx ONAIR.medialibs)
• Additional Cartwall Libraries (file ProppFrexx ONAIR.cartwalllibs)
• Additional Script Libraries (file ProppFrexx ONAIR.scriptlibs)
• Global Message Center Messages (file ProppFrexx ONAIR.messages)
• Mixing configuration (file ProppFrexx ONAIR.mixing)
By default ProppFrexx ONAIR stores the above mentioned configuration files in the standard configuration directory (which might be either the default Application User Data Folder or the configuration directory as defined by the -config command-line option, see above).
By using this command-line option you can enforce ProppFrexx ONAIR to retrieve and store the above mentioned configuration files at the given path location. This might for example be useful, if you want to share a global and common configuration of your libraries and mixing settings for different ProppFrexx instances (e.g. installed on different machines within a network) at a single central location. When doing so, be careful with making changes to these global config files, as different ProppFrexx instances might overwrite each others changes. To prevent such scenario, make sure to use a single dedicated ProppFrexx instance for making changes to your library collection (add or remove libraries) and for making changes to your mixing settings.
Attention:
Before using the -globalconfig option do the following:
a) create a global shared config folder
b) copy the existing files into that new folder
AND make sure to also same your media libs (playlist) as well as script files to a shared location, which is accessible by all instances.
That's it.
So basically the above -globalconfig command-line option will do the trick!
For manual syncing (reload) you can use the related control-commands:
MAIN_RELOAD_LIBRARY, MAIN_RESCAN_LIBRARY, SCHEDULER_REFRESH, ADVERTLIB_REFRESH