Once you define a string literal in a variable it stays there
You can however manipulate “output”.
Printing: Txb Text(2:3)
Or “input” in sofistik commands: Lc ... Title "Loadcase nr #var(1)"
But there’s a lot of trial and error.
Use dbg#2 to understand what you store, e.g.:
+PROG TEMPLATE
DBG#2
LET#TEXT 'ABCDEF','LMNOPR'
TXB #TEXT(2:4)
END