I’m a little confused trying to create an expression text (like molto apassionato or cantabile) which is neither a dynamic or a tempo change. I tried Shift+X but I need more control over which layouts it will show. For example, sometimes I need a text that shows only on first staff in Full Score layout but also in every other individual layout. Could you guys point me to the right direction?
Shift+X produces staff text, which displays over a single stave; you’re looking for system text, which is Shift+Alt/Opt+X. By default, it behaves the same way as tempo marks in terms of where it displays, but you can tweak this in Layout Options > Staves and Systems > System-attached Items.
In addition to @asherber’s answer I recommend to create a paragraph style for the expression and save it as default (clicking the star). Then it appears in both Create Text and Create System Text menus and you can assign keyboard shortcuts. If you need those expressions frequently this is a time-saver.