The multiple keypress command is limited to 6 characters at a time. So you would have to send several sets of commands in a row. I never had luck with this due to timeouts or buffer overflows. Also there is no error checking. The TPI manual specifically warns against using this command with installer code:
Using the TPI commands 070 and 071, you can conceivably put the panel into installers mode (*8). The danger here is that when in installers mode most of the commands are locked out so you could end up dead-locking yourself with the only way out of installers being to power cycle the panel.
I am not quite sure what you want to accomplish. The keypad itself already makes a beep-beep-beep sound when the alarm gets disarmed. And you can have the keypad countdown beeps until the house is fully armed. Combined with a control page that shows me the armed status of each partition I don't have the need for a bell squawk. And wrapping a towel around the siren would totally defeat having a security alarm at all.