There's no native support for it, no.

The only option remaining, which is a bit dangerous, is to use the writable_schema pragma.
You allow it, edit sqlite_schema, i.e. SQL UPDATE sqlite_schema.sql for the table you want to modify,
by using textual substitutions in the DDL, then reset writable_schema, which forces SQLite to reload the schema.

And if you mess up the edit, your DB is toast :).

Of course, the edits you make must be innocuous to already inserted data, their indexes and constraints.
Sounds like yours is in that category, so it would work fine.

I've successfully upgraded DBs using this technique, messing up many times until I got the edits robust enough and just right.

The safe alternative is of course to create a new table (or DB) with the new DDL, and transfer the data over.
The above is only if you want to do the upgrade in-place, typically for (very) large tables.

So start with the safe approach, see if it's fast enough for you, and only if it isn't, reach for the foot-gun!