I've imported a CSV file having the first column to be date-time values in ISO 8601 format like

2012-01-01T00:00:00.000Z

for the first moment of the year 2012.

Then, willing to make LibreOffice to recognize the format (as I was looking forward to plot a diagram), I've selected the column, chosen Format Cells... and entered the custom time format as

YYYY-MM-DDTHH:MM:SS.000Z

And this seems to work if... I edit a cell to remove a hidden single-quote from its beginning (which serves to protect a cell content from being interpreted) as all the newly formatted cells now store values like

'2012-01-01T00:00:00.000Z

(note the single quote - it is only visible when you edit a particular cell).

And I am to do so for all the cells in the column. How can I automate this?

UPDATE: I've already found a solution for the particular case of mine: it helps to set a column format to "time" in the CSV import dialogue. But I am still curious how could this be done in case I wouldn't have the original .csv data file to import but only the .ods file with the data already imported without the format specified at the import time.