If you have "write" privelege to a field due to your auth level and the FieldDesc, you will see lines like this when you edit pages:

/set field1 ?= value list ...
/set field2(subkey) ?= value list ...

You can use these to edit fields, but you must change ?= to =

When you save the page, these are processed if the first word is "/set" and the third is "=". Omit (subkey) if no subkey (i.e. empty subkey).

Setting the list to empty deletes the field record.

If a field does not exist, it is not shown. You can add it.