Begin/End Rules for Monthly and Yearly DiaryGridLines
If the template selected for the current DiaryGridLine was defined as a monthly or yearly template, then editing either of the begin/end rule properties brings up a property editor which allows you to select a Month and a Year Offset for monthlies :
These settings are analogous to those for the daily/weekly diaries. For yearlies, only the year offset is necessary, the month is ignored for yearly diaries; only the Year Offset is taken into account.
Note that whether a monthly diary starts on the first of the month, or at the beginning of the week of the first of the month, is determined by the way you defined structure of the scanned GridTemplate.