Summing up, I don’t see, based on the discussion so far, a need for a new “adjust cost basis” operation, because everything can be modelled by existing operation, which are already too many in PP.
The weirdest one isthe “transfer” - one might think it’s equivalent of delivery outbound from one account and delivery inbound into another, but it’s actually not, because people expect that it maintains the original date of the original (non-transfer) transaction: Berücksichtigung des initialen Anschaffungsdatums bei mehrmaligem Wertpapiertransfer - #15 by Rafa . Just think about it: a transaction done at date X should behave as if it was done at much earlier date. That’s weird. I wonder if all the time-related performance calculations in PP are correct in regard to that madness, because transfer date is clearly not fully correct, as that thread shows.
Bottom line: if someone comes up with a usecase where the original opening date is important (e.g. for future reordering), then Deliver Out/In idea falls apart, as it clearly doesn’t preserve the original date.