No, that would be to arbitrarily protect the most polluting of farming practices. The key is defining a transition from the status quo to the ideal where allocations are made on the basis of best practice. So that’s a tradeable market for rights. So grandparenting of rights in perpetuity would not be a goer, but a defined and reasonable pathway will be necessary.
The other problem with grandparenting is that it gives a terrible incentive – valuable rights to pollute are handed to those who do it most. This means that those land users who improve farming practices or have chosen to use less intensive farming methods are penalised.