How to rename a field and have the existing data stay in it

I figured out I should have named a field differently to make it directly usable when the KBT data is imported in specific GPS devices. Renaming a field is easy, but how can I get the existing values in my hundreds of existing collected points stay in this renamed field and not switch in a field with the older name? Editing every line through the spreadsheet view is not an option regarding the number of points I have and the very slow UI when editing a line.

Unfortunately what you are asking for is not possible, the data collected on the previous name will remain in that name.