Note: All Excel protection is relatively weak. It is useful to stop casual users but it is not for top secret information.
You can lock cells but allow colour formatting or comments which don’t affect the security of the formula but allow a user to provide some sort of feedback to you. Note that adding comments is different from formatting so it requires a different setting.
To follow along go to 19.5
If you want to allow a user to change the format of locked cells (e.g. make it red if they disagree or have a question), you need to specify this in the Protect Sheet options. Note below that by ticking on the ‘Format Cells’ we are able to turn a protected cell red.
If you want to allow them to add a comment, you need to switch on a different setting. Again this is in the Protect Sheet options. If you scroll down you will see an ‘Edit Objects Setting’. With this on you will allow comments to be added.