I have an alternative pedal marking (signifying to press the pedal violently in order to make the strings vibrate so much that you hear it). I hoped to make it by duplicating and then adjusting the ordinary pedal marking. That is impossible, maybe? I did not find sustain pedal among the available playing technics.
Nonetheless: I have looked for a way to make my peal marking always appear under the left hand, also when I enter it into the right hand, like for ordinary pedal markings. Is that possible?
Go to Engrave mode, then Engrave > Playing Techniques and build a new Playing Technique that contains whatever glyphs you like. Ensure that you set it to show Below by default.
The only way you can ensure it always shows below the bottom staff is to apply it to the bottom staff. Even if all of the bottom staff notes are cross-staffed up to the top staff, this isn’t a problem - just make sure you enter the Playing Technique with the caret on the correct (bottom) staff.