I know in bitbucket and others have a nice feature that allows you to edit code inline on the web browser and commit the changes - wouldn't that be a safer approach than editing via commenting? I don't think it would take much more time either.

Maybe doing the reverse, if a change is made through inline edit automatically add a comment with the specific change made.

I just can foresee undesired consequences. Someone not escaping their sed correctly (I.e. they try to replace a string with a slash or apostrophe)