The solution to the problem is going to be entirely different for another headphone, especially as the M50 uses a dynamic driver, while the T50RP uses a planar magnetic driver, so tuning these driver types needs a completely different approach.
Having said that, successfully tuning dynamic drivers is much harder to achieve than planars.
There are some 'brutal' methods of taming treble like adding thin foam or some thin felt/cloth to the ear-side of the driver baffle.
But this usually has certain trade-offs that come with it, like reducing over-all resolution as sound is being blocked from reaching your ears so easily.
Sometimes this can also bloat the bass or you just end up with a muddy sound.
You may want to simply try the reverse approach and increase the bass, which I have found is much easier to achieve.
Usually adding a ring of thin foam or thick felt around the driver baffle ear-side (but not covering up the driver) usually increases bass volume.
It will usually get slightly bloated or muddy, but you won't know until you try.