Two versions of full score

Is it possible to have two versions of the Full score within a project? i.e. an A3 size version and an A4 size condensed version. Otherwise swapping between the two requires rebuilding the title page.

Sure. Just create a new score layout from the right panel of Setup mode, then set its Layout Options accordingly (and perform any necessary graphical tweaks).

Depending on how the title page is constructed, you may still have some rebuilding to do, though.

You can also rename the layouts if you want to help keep track of them (e.g. “Full score (A3)” and “Full score (A4)”) although if you use the {@layoutname@} token in the score, that will be updated as well.

Related to this thread:

I will need two scores for a client. I’m not sure whether to make the second score a using a Part or a Full Score layout.

Are there any pros/cons for either?

Eg I know that many paragraph styles have a separate font size for score and parts.

Eg If I recall correctly, changing enharmonic spellings in a score would do it everywhere whereas in a part it won’t. What if there are two scores?

Would love some guidance

Other than setting a few defaults like staff labels, I’m not actually sure there’s a difference.

The essential differences are listed here in the docs. I would make it a score layout … unless you need any different enharmonics in the second score.

I wouldn’t really see that much of a difference, but you think of it based on how you idealize, not what method you start as.
Enharmonic spellings would do it wherever you set local properties as, either local or global, for that moment. You could also use propagate properties.
Hopefully you’re not doing this for an orchestral score. If you are, you will probably get smacked on the head by the conductor, because having different note names on fullscore and part is a nightmare for communication later. Imagine the horn player in F reading a D flat, which sounds as a G flat, only for the conductor’s score to be in transposed pitch, but the note being a C sharp instead.