John, yet again I missed the budding workshop…

But the problem with (Bud) top-working “mature trees” is the thickness of their bark. You need to insert the bud so it will protrude beyond the bark while sitting flush against the cambial layer. When the bark’s a quarter inch thick and the bud’s about the same, I don’t believe it works.

You can of course find a younger limb or stem, but they’re generally so far ‘out on a limb’ as not to be a decent place for a new variety. Also, lots of sunlight is needed to spark the vegetative growth and that’s not easy to find with a mature tree.