There were programs floating around that let users inject special characters directly into their source code (RMG_IME might be one of them?) but I don't know where they are these days.
Methods of accessing a third minidemo within EX8TECHDEMO are completely intact, but no such demo routine exists! Was this something cut during development, or reserved space to add another demo later?
Additionally, I checked every entry of the autocomplete (yes, every one) and I found two more keywords that are unreserved (you can tell because they aren't highlighted). TO and STEP can be used as names for anything without restriction, which means code like FOR TO=0 TO TO STEP STEP can get past the parser. Yikes.
Thanks for the further research. Another addendum:
DEF blocks for commands that take the name PI are allowed and will work as expected, only functions are ignored (except in the CALL case, apparently).
The function PI appears not to be reserved. It does not get highlighted in the editor, and DEF blocks named PI are ignored without throwing an error. However, DEF blocks still cannot overwrite the PI function. This code will still print the proper full result of PI().