It depends on whether they would offer the same promotion choice or a different one. For the same choice all you would have to do is add the line
maxPromote=2
to the Diagram definition, and make sure the two promotiong pieces are the first two in the table. It doesn't matter what their ID is; only the IDs of the pieces they promote to must be used in promoChoice, never the ID of the promoting piece.
Offering a different choice is possible in the Diagram, by only have the first piece promote normally (the default situation), and defining a second promotion set, and letting the second piece morph to that. But this is not supported in the GAME code yet; only automatic morphing into a single type is supported there.
It depends on whether they would offer the same promotion choice or a different one. For the same choice all you would have to do is add the line
maxPromote=2
to the Diagram definition, and make sure the two promotiong pieces are the first two in the table. It doesn't matter what their ID is; only the IDs of the pieces they promote to must be used in promoChoice, never the ID of the promoting piece.
Offering a different choice is possible in the Diagram, by only have the first piece promote normally (the default situation), and defining a second promotion set, and letting the second piece morph to that. But this is not supported in the GAME code yet; only automatic morphing into a single type is supported there.