Yes, you can just use "+" between two strings in the expression syntax.
You can set the result to a string or you can append directly inside a print.
You can also append in a dynamic string reference too (not demonstrated below).
start_at = start
locations { start; }
strings { tmp : string ; }
integers { seven : integer "7" ; two : integer "2" ; }
on_startup {
: print {("This " + "is " + "a " + "built " + "string ("+(seven+two)+")." )}
: press_any_key ;
: set_string var = "tmp" {( "This " + "is " + "a " + "built " + "string ("+(seven*two)+")." )}
: print "{tmp}" ;
: press_any_key ;
}