I would like nothing better than to tell you that you can convert your home into rental property after 36 months, however, the first link I sent you,
is directly from the horse's mouth, the IRS, and their chart was very specific.
In both circumstances (turning the property into rental either before OR after the 36 months) you will have to pay the credit back in a lump sum in the year that you convert the property.
As for the IRS knowing that you either sold early, or that you converted it to rental property:
1-you had to include the HUD statement to get the credit, that means that the IRS has the address of your property. so if you sell the property, it will be recorded with the Register of Deeds.
2- if you convert the property to rental, you must include the address of the rental property on the form 1040 Schedule E..
Although the IRS will eventually get these reports, the fastest way that the IRS will be notified is via your change of address at the post office.
I understand that you may be disappointed by the Answer you received, as it may not necessarily be favorable to your situation. Had I been able to provide an Answer which might have given you a successful legal outcome, it would have been my pleasure to do so.