For const/perm loans you have the option to report them at origination or when it goes to the permanent phase.
For a construction/permanent covered loan, the institution reports either the closing or account opening date, or the date the covered loan converts to the permanent financing. Although an institution need not choose the same approach for its entire HMDA submission, it should be generally consistent (such as by routinely using one approach within a particular division of the institution or for a category of covered loans). Notwithstanding this flexibility regarding the use of the closing or account opening date in connection with reporting the date action was taken, the institution must report the origination as occurring in the year in which the origination goes to closing or the account is opened.
Since you modified the 5/1 ARM const/perm to a fixed rate, assuming before the permanent phase kicked in, it would be my opinion you should report the loan as of its origination date.
The opinions expressed are mine and they are not to be taken as legal advice.