The standard follow-up flags are: “Today”, “Tomorrow”, “This Week”, “Next Week” and “No Date”. I’d like to add another option to this list for “This Month”.
Yes it is, and I did it!!!
Source: windows – Is it possible to create custom follow-up flags in Outlook 2007? – Super User | https://msdn.microsoft.com/en-us/library/office/ff865785.aspx