.csv paste and format issue on

sorry my first time put all the detail in the question section
i am editing data for MySql therefore using .csv the problem i have is when the csv file is open it wont allow me to paste into a columm or a cell. to get paste to work i must close the file and reopen it but alas when i reopen the file it has chaned my date and time colums to number th\erefore i must reformat again agh could do with some assistane thanks in advance