I’m flying this route on Dec 13 and I’m now wondering if it will be switched to a Wamos plane.

How many days before the flight do they usually announce if Wamos will operate the flight, or does it just happen on the day?

The Wamos A330-200s with identical J seats to IB seem to currently be flying for LATAM and Philippines Air. EC-MAJ which is currently doing the PTY flights looks to have a terrible J cabin.

Iberia is showing Dec 11 as Wamos, but Dec 12 onwards as Iberia itself. Will keep an eye on it.