Hi Italyuser, just keep in mind that this can make the line difficult to read. I once performed from an edition of Brahms’s LIebesliederwaltzer that printed the vocal parts (all of them) at cue size, and was squinting at the page for weeks. It’s probably a fine idea if your soloist has a part of their own, as is often done with instrumental soli in choral works. Just a friendly suggestion! Good luck with your piece!