Looking on historical data from Yahoo there is a good deal of mistakes. It is easy to delete but when I update the data on a daily basis it downloads all the old data again. Is there a way to correct and save old data and easy upload new data? Do my question make sense?

Question doesn't make much sense to me as the Yahoo! provider does not overwrite your edits. Perhaps it's too general and lacks examples. The Yahoo! provider may apply corrections to the last 10 bars but that's the whole depth it can affect.

P.S. Make sure to uncheck "Automatically update data for symbols on demand..." in the Data Manager.

OK let me try to be more clear.

I download the data for Nike. There's about 10 mistake in the data. I simply delete the mistake. Next day when I download the new days data into WL I reload Nike and open it. Now the old data from Yahoo is back and my edits gone. Thus I have to go through the chart again and again edit the mistake.

Can I edit one time and then load the daily data in another way than reloading the full data series?

Of course you should not reload the edited data - neither by right clicking on the chart and selecting "Reload chart history" nor by using the Data Tool. Except for Wealth-Data which has a unique feature "Keep user's edits on data reload", with all other providers this will always result in a complete overwrite of the data.

Now you keep your copy which is believed to be more correct than the source. Simply update the data either way (Update DataSet / Update All Data) but don't reload.