Im using the custom fact just to make my custom tags.
Made it like a code system and I used the userdfined translation to show proper name for the tag.
Having ex. a DEPT which cover a list in the churchbook where the priest wrote down people who came or left the city (the standard tag covers people who left the country imo). Using the standard MARR to cover marriage which are not related to me (way to make it more simpel to me not having a huge amount of halfsiblings and familytabs). Having also a COURT which cover some supreme court facts where I can link to the media with the case.
So as Nigel suggested use the custom fact and you will not get into trouble with the standard gedcom tags 🙂
Regards, Jamie Jaconelli
admin and owner of: www.jaconelli.dk/webtrees, www.jaconelli.dk/history, www.jaconelli.dk/johnsen (familien-johnsen.dk)