I tried this using excel 2016
I opened Excel - Select File,open selected the "CSV" file and selected delimited, Semicolon as the separator and " as the text delimiter.
This was then imported as expected and I could edit the cell and delete the L as per you original question
Clicking SAVE does corrupt the file as you found and explained in other answers.
However select SAVE AS and selected UNICODE as per one of the comments - the file was saved UTF-8 as a TAB separated file with " as the text delimeter. Have you tried this? Is this not acceptable?
If I selected SAVEAS and selected UTF-8 Comma Separated then it was saved UTF-8 comma separated - I could not see a method of retaining the Semicolon as separator. You should however go through the SAVE AS options and see if one of the formats available in your version of Excel is acceptable.
If it is necessary to retain the semicolon then you could post process the saved file a text replacement script that understood quoting (so that , inside the quotes don't get replaced) A VBScript or Powershell script could be written to do this, alternately a VBA macro to concatenate all the cells into one cell with commas separating them could be used.
A single line Powershell dependent command to to that final conversion would be (Run from CMD prompt)
powershell -command "& import-csv 'CSVUTF.CSV'| export-csv 'PSCSVUTF.CSV' -Encoding 'UTF8' -Delimiter ';' -notype"
If your file does not have a header line with column names then a -header parameter will need to be provided and the output file will end up with an header line