Is it possible for a WO to reclassify to a different MOS?

Each warrant MOS dictates it's own prerequisites.
Warrant MOSs don't do Reclass. Reclass is essentially being told you had a new MOS and you will attend the training on a certain date.
Warrant MOS is being told you meet the prerequisites of a certain MOS and you are being allowed to attend training.
So, unless you are applying to a warrant MOS that currently accepts warrants, there is no Reclass. Alternately you can resign your commission and Reclass as an enlisted soldier.

Only warrant reclass I saw was a medically DQed Chinook Pilot they made a Mobility Warrant.

Based on 26 years of old experience seeing deep in the regulations that you can reclass a helicopter repair specialist to a wheel vehicle mechanic and that commissioned officers i’m Sure there’s some way a warrant can change specialization. Flight from a maintenance mos would be my first clue. Hopefully some CWs that are SME can clairify further!