I ran into this with the recent T.Rowe mutual funds and their migration to lower ER funds, but with different symbols. The download merely had the usual REMOVE Shares for ALL the old symbol, and ADD Shares for the new symbol.... pricing is slightly different.
But just doing that looses all the prior history related to the "old" symbol...
SO, any suggestions on how to change the "holdings" with the new symbol,
but still somehow retain all the old history and prior transactions cost basis -