Use freeform text; it's a standard part of musical notation. Just because most of what you see on a score is some form or another of shorthand doesn't mean everything is.
How do you think Tom Lehrer was able to indicate a tempo of "Pornissimo"?
https://tomlehrersongs.com/wp-content/uploads/2019/02/smut-m...
The only real problem is guitar always has several different ways to play the same notes all over the neck and instrument tuning isn't always specified either.
Standard tuning may not work and tabs sometimes aren't there alongside the staff. If you're trying to sight read, you'll guess alright for a while until you are suddenly forced to make heroic leaps to the other end of the neck or painfully contort your fingers just so you don't miss a beat.
But also, really, I was always taught that unless the composer specifies something specific, you are free to figure it on your own. Like there are only so many contexts where the timbral differences between two unison, fretted notes is going to matter probably, right? Also, how you play some part might be informed by where you are after the preceding part etc.
Tuning point though is kinda interesting and not all my wheel house. But they do call the default one standard for a reason!
With regards to tuning, fingerstyle will often feature an arbitrary tuning unique to only a handful of songs. Timbre absolutely matters because you're playing multiple parts on one fretboard simultaneously.
Here's an example of all three genres in one performance! Kent Nishimura covering Steely Dan's "Peg" in fingerstyle. He does have a book available. It combines ordinary sheet music with tablature.
probably a standalone Italian word would be fine, or some special < like we have for gradually increasing volume