Adding symbols to palette- again, and again. Button accordion row marks.

Button accordion. Here in Finland we use terms "Inner rows", it is three row from bellow. I school notes we mark it as "S" with circle. Three middle rows are "middle rows" and we use mark "K". And three last rows are "outer rows", "U".

So,
Inner rows = Sisärivit = S with circle round.
Middle rows = Keskirivit = K with circle round.
Outer rows = ulkorivit = U with circle round.

It is easy add this as "ctrl+T" and drag it to suitable place.

But. Most flexible is add this to own special palette. But how? I try make own palette and I add fingerings to it. 1, 2, 3, 4, 5 are ok, of course. But free text not. I try add text "ctrl+t" to note and drag it to palette. Not work. Drag with Ctrl. Nothing.

So- how I can add this "S", "K" and "U" to own palette?