"It seems clear to me that the Buddha would not have been averse to later doctrinal innovation if it occurred within the fundamental structure of the Dharma, that is, if it was of spiritual benefit on the path to nirvāṇa." - 1989 version of his Mahāyāna Buddhism, pp.11-12.This comes just after another quote worth copying in full - but I'm too lazy at the moment so lets just hope this link works for everyone.
The gist is, I think, in line with what many people argue about Buddhism, that it is anti-essentialist and thus, in a sense, hard to pin down. It does however set a criteria for change: that those changes are helpful/useful. If a doctrine no longer helps, it is to be discarded. Vigorous debate and analysis would thus seem to be encouraged, so that each new generation of students learned for themselves and understood for themselves the truth of things - rather than ever relying on teachings alone.
'Tis worth noting something else Paul writes (on p.3) regarding anti-essentialism in Buddhism [directly in regard to the essentialist fallacy of trying to lump all of Mahāyāna under certain sweeping labels]:
"An ability to look behind unities and see them as merely words, convenient but misleading linguistic constructs, has always formed an important factor in developing insight meditation, the spiritual cultivation which alone will lead to seeing things as they really are, the sine qua non of nirvāṇa, enlightenment, the cessation of moral obscurations and ignorance."The lesson? While there is no absolute right and wrong out there for us to grasp onto, there are right and wrong (kusala/akusala) moments and ideas for us. Things that are not helpful, not morally wholesome, not conducive to wisdom --- these are wrong. That much we definitely can say about Buddhist ethics.
But we cannot say one MUST meditate, or tithe 10%, or live in a monastery, or this or that... If we know that meditation, generosity, etc will be helpful, wholesome, and/or conducive to wisdom, either for others or ourselves - then we may say they are right and should be done.
This distinction is crucial and should be understood (there I go with my shoulds!). Our ignorant habit of clinging wishes to find an Answer out there that is right and always right and never changing. No such answer is to be found. But there are "a" answers out there, moments of truth, concepts that help, suggestions and even stern admonishments that break us away from our unhealthy habits. These are right, but they are only right in that very moment. Tomorrow they may no longer work, they may in fact be wrong then.
Who knows? Do not cling...