Write in excel file that is in read-only mode

I would like to write in an excel file. However, this excel file is in read-only mode on purpose. How can I write in this excel file ?
I don’t want to manually remove the read-only mode, as I have lots of read-only excel files to work with.
After writing in this excel file, I would like to put it back to read-only mode.
Best regards

I’d prepare two VBA macros and execute them:

To set ReadOnly=True
SetAttr “C:\Blank.xls”, vbReadOnly
To set ReadOnly=False
SetAttr “C:\Blank.xls”, vbNormal

Thank you for the answer.
I am not familiar with macro: where should I put the code ? In all the files where I want to write ? Should I make a dynamic variable in place of “C:\Blank.xls”?