No way to get into or out of ALT mode remotely etc.
Just to be clear, you cannot send key presses to CHDK from chdkptp, script key presses always go to the normal firmware. You can use =enter_alt() and =exit_alt() to change alt state, but you can't navigate the CHDK menu with key presses or anything like that.
Most keys are ignored by the normal firmware before you switch to rec mode, unless you send
=post_levent_to_ui(4484)
The direction and menu keys should work after you switch to rec.