Hi Houstonwb,
To manually correct a dividend, use the
Data Register. If you edit a reinvestment, and change the number of shares, that will change the share balance going forward. However, it will not change the amount/shares for already recorded future dividends. You would have to re-retrieve those, or edit them. When retrieving dividends from Yahoo, Yahoo reports the dividend/share amount, so to get the total correct dividend value, you do need to have the correct share balance recorded at the time of retrieval.
FM should retrieve the full resolution of the dist/share as reported by Yahoo. You might compare what Yahoo is showing to FM in the Data Register, and make sure you have the display resolution turned up on price. See "Options / General Preferences... / Display / Price Digits", and set it to 6. If Yahoo is showing more resolution that FM retrieves, please give me an example ticker symbol/date.
FM won't delete investment files from your hard drive. You can only "close" an investment. If you want to delete the file, you'd have to do that yourself in File Explorer or something similar.
With Yahoo (Historical) there is no option to only download dividends, you always get prices too.