Hello bal,
..is it possible to convert to a 13 month fiscal year when you move to Adagio?
The quick answer is... "perhaps"
If you want to use the 13th period for year end closing entries, then this is a fairly straightforward process that can be done by any database repair company (including Softrak - but not for free). If you do not care about the transaction details, then you could create and empty database and import the 12 net posted figures yourself from your 12 period Ledger.
If you are trying to move from 12 monthly periods to something along the lines of a 4-4-5 fiscal calender, then this is a much more complicated process (if it can be doner at all).
Does that help?