Not really, if you type over a cell, its original contents are lost....
You can incorporate a sort of error handling statement into your Vlookup though:
=IF(Vlookup(value,range,offset,false)="","your comment",vlookup(value,range,offset,false))
Both the Vlookup statements are the same, if it returns a "" (blank) value, your text will be displayed instead....
I have used it with "", isna, iserror, its quite effective at removing grubby looking errors off your sheets!