filters are in the file flt.dat, you can backup them but not to save them one by one. as to joining different flt.dat files i'm not sure i need to check it whether it is possible.
It would be nice if you could
a) add an option to export the filters in a txt or csv file and
b) sort filters by name (in order to check them and add desired filters) - I know duplicates are shown in red...