That’s not how MIDI works.
With MIDI v1.0 (the common version in use for the last several decades and still in common use today) you cannot have a velocity of more than 127. Period.
There is space (7 bits) for 0-127 and that is all. “…the velocity is beyond the limit (i.e. 127)” does not actually make technical sense as the number cannot ever be above 127.
When you see the volume bars in Ardour you are seeing (as I understand it) an estimation of the result of the MIDI being rendered locally by a MIDI instrument plugin. I’m not sure what the mapping is, but it sets 127 to be well above 0 dBFS (it looks to be around 6 dBFS to me), as can be seen on the meter (note the 0 and 127 markers):
You can adjust this using the track mixer if you like, so it doesn’t go into the red.
EDIT: I think it also depends what MIDI plugin you have (if any) inserted onto the track. If you have a MIDI instrument plugin, then Ardour renders the MIDI notes into audio, and I think the track level bars represent the resulting audio. Different MIDI plugin instruments may result in different output levels.
If these are “hot” then the only harm should be that the resulting audio from Ardour sounds too loud, or is distorted on playback.
If you don’t have a MIDI instrument plugin, Ardour metering reverts to a simple display of MIDI velocity level.
If you connect the track MIDI output to an external MIDI instrument, like your Disklavier, it will use standard MIDI codes, including the 0-127 velocity, so it cannot harm the Disklavier. In this case, the Disklavier will take the MIDI and render it to produce audio.
Note that there is a MIDI v2.0 specification that is fairly recent. That has much higher resolution parameters, so you will be able to have velocity greater than 127. However, greater does not mean louder. It just means there are more steps between maximum.
MIDI 2.0 is currently only supported on a handful of equipment and software (as far as I know, it is not supported by Ardour yet) and is not directly compatible with MIDI v1.0 equipment. For a start, it won’t use 5-pin DIN connectors, so there is no danger that you accidentally send MIDI 2.0 data to a MIDI 1.0 device. And even if you could, it would be unlikely to harm it.
I hope that helps.