Hi Vweetly,
It is not feasible to remind user can’t edit the file as another user was in the same file when user open the file.
If you didn’t set “Allow change by more than one user”, you couldn’t upload your change when there is another user was in the same file.
You can refer to the following article:
About the shared workbook feature
Given the situation, we suggest you vote for your requirement to UserVoice, which will help better our products and services.
Thanks for your understanding.
Qing