How to use Lot generation at Item level for few items and User Defined for few

Summary:

We have around 100 Items, Out of 100
1.we want to use Lot generation at Item level for 2 items, so user can click on "Generate Lot Button" and default lot from Items setup
2.We want to use Lot generation as User Defined for remaining 98 Items, so user can enter whatever lot they have actually.

Currently, we are using Lot generation at item level, so we can default lot from item setup as well as we can enter lot manually for item, we don't want generate lot automatically.

Any other approch can help here?

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