Up to 15 tickers make up one shared comparison list, the choices the "vs" menu offers wherever the app can overlay a benchmark. There is only one list, not one per chart: it opened out of Settings → Charts into its own editor, reached from the "vs" menu's Edit list… on the Dashboard's Portfolio Value chart and from Allocation models' Backtest tab, and an edit in either place is what both charts show next.
A ticker typed here that the app has never seen is added to Securities & prices and priced automatically, a consequence that is not obvious from a text field that otherwise just reorders an existing list. Search your holdings or type any symbol; the optional label is what shows in the "vs" dropdown in place of the raw ticker.
The default benchmark field beside the list pre-selects which of those 15 tickers the Dashboard and the Backtest tab show by default; either chart can still override its own pick for the session without changing this default.
During an expired commercial trial the list stays editable, but only halfway. Reordering, relabeling, removing a row, or picking a ticker the app already knows all save, none of them write a new fact about a security. Adding a ticker Securities & prices has never seen is refused instead, because that write registers a new ticker record, which the trial gate protects; the field explains the refusal in place rather than pretending the save succeeded.