Hi Ollie,
I agree, it sounds like the classic symptoms of over-watering and hopefully now with your new regeme, the Yucca will soon be back on the road to recovery!
Yesterdays yellow, useually turns out to be tommorows brown, so you may as well cut back beyond the yellow too.
Cut with scissors from each side, at an angle so that the leaves have a point (they will look better and recover quicker too)
If the light levels where low then, yes this may also have contributed to it looking poorly.
If you have the option of the conservatory, I think it might fair better in there, as they do prefer good light.
Good Luck. Tbird+