Nah it was more than a change in approach.
Look at it this way, Martial's output is respectable but his game time isn't. That's because despite Martial's numbers, Mourinho wasn't satisfied with the way he was playing the role given to him and maybe because Martial wasn't displaying the adequate mindset around the training pitch.
Martial's personal problems existed under LVG, so you can't really consider that only Mourinho had to deal with it and LVG was perfectly happy with Martial's performances on the field, so logically the main problem is that Mourinho wants something different from his wide players and strikers, something that Martial never had in his locker. Martial isn't an anchor(I prefer that term to target man) or a winger.
There is only three outcomes here, either Mourinho starts using Martial to its strength or Martial learns the roles that Mourinho likes or Martial is out.