//! external

What programs are used with //! external directive.
I know only about ObjectMerger.
Are there any other uses?

Pretty much everything that is included in PitzerMike's Grimex.

1. File importer;
2. Path mapper;
3. File exporter;
4. Tile setter;
5. Object merger;
6. Constant merger;
7. Trigger merger.

Note that some of these (such as the tile setter) are much more conveniently used from the WE itself (found under the "Extensions" menu).

Does each of those require map save and reopen?