Can anybody tell me if it is possible after opening an excel sheet in
readonly mode to switch to write mode?

to be more specific.
I have a schedule in the team with a password to modify.
if someone else has it open for writing, I can choose at opening for
notify.
the moment the other person closes the sheet, I get a message and the
possibility to login with the pw, without closing the sheet first.
Now I wonder if this is also possible when I open the sheet (only me,
nobody else) choose for Readonly and then later I want to switch to
write, whitout having to close the sheet.

Is this possible?