The ship was larger but if it's only to be used for the Queen's landing it's okay the living quarters and the cockpit area seem to be the same size (I think they used a plate from the TPM ship to created the interior in AOTC anyway).

It might be cool to replace the silverbird with the Republic cruiser anyway though that would be a lot of work.

I can't really see the point myself.

In terms of story telling (especially if the scenes are to be rearranged) it makes more sense to swap the Republic ship with the Queen's ship and have the Royal party return to the planet in escape pods before her ship lands on the Fed ship.

There are real world examples of elected monarchs serving fixed terms BTW.

I never had a problem with that aspect of an alien culture.