Yes, it is going to get overwritten by what the Quotes provider uses based on the ticker.While we don't have control over how the Quotes provider operates, one thing that would be very helpful here would be able to display the symbol in Investment account registers. That way you could see which are the B, C shares, etc. You can display the symbol in the Security list, but not in the register view.
What version Quicken for Mac are you using?Do you download from your Fi? If you do the names in the security detail cannot be modified