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.