I dont think this is Inonotus hispidus, it looks more like a species of Ganoderma. The brackets are quite easy to tell apart:
Inonotus hispidus is fleshy, leathery, hairy on top. It is annual, appearing in summer and gradually rotting to a nasty black mess which persists into the winter.
Ganoderma species are hard and wood-like, not hairy. They are perennial and every year they add a new layer to the edge which is white at first, becoming brown. There are several similar species, you cant tell them apart from a photo.
It is relatively immaterial, except to mycologists, which species or even genus is attacking your tree. Bracket fungi enter the dead heartwood of trees through cracks or pruning cuts and grow there, feeding on the wood and decaying it in the process. Eventually they grow out to produce the bracket-shaped fruiting bodies which liberate airborne spores.
Bracket fungi do not kill trees because they do not attack living bark or sapwood. However, the decay weakens the structure so that the branch or the whole tree may fall. If it doesnt it can become completely hollow which is very good for wildlife. If your tree poses a potential hazard to people or property you should take steps to make it safe, either by cutting back, or bracing or propping it in some way. Gardeners are responsible in law for the safety of their trees and you could be in trouble if it falls on the postman or the neighbour's shed.
Because the living parts are unaffected the tree can go on producing apples for many years. I would therefore assess whether it poses a hazard, brace it if necessary and let it be. There is no point in removing the bracket, when spores are in season they blow for miles and the air is full of them.
You mentioned honey fungus, which this definitely is not. Honey fungus almost always produces its clumps of honey coloured toadstools from the base of the trunk, or from infected roots below ground, for a few weeks in the autumn. Honey fungus enters the root system below ground and very rarely spreads up the trunk. Apples are very susceptible, but as with brackets, trees may live for many years with infection in the roots. Even when the weakened roots fail and the tree falls, it may live and go on producing apples for many years as long as some roots survive.
The tree could quite possibly have honey fungus infection in the roots as well as the bracket fungus in the trunk, but there is no evidence of it in your photo.