Can I include more than 9 indicators in the NNFX Algo Tester?

No. With the NNFX Algo Tester you can add up to 9 different indicators to your algorithm.

Some indicators, like ATR and Baseline have specific functions (money management and basic trend indicator respectively). The C1 (main confirmation) serves as an entry indicator, that is, it creates the entry signal. The remaining indicators serve as confirmers for the entry signal, and you can change their operating mode if you want.

And even though it is possible to change the function of some indicators, it is not possible to backtest more than 9 indicators at the same time. You can ask a programmer to merge two indicators into one.