NBIC makes it very clear that this alteration (re-rate) may be performed using the edition/addenda of the original construction or a later edition/addenda, whichever is most applicable to the work being performed. (This is very clearly stated in the interpretation section of NBIC. I don't have my book with me, but I believe the interpretation is from '95).
It is perfectly acceptable to perform the re-rate using the edition/addenda of ASME code that the original equipment was built to--this means that you may use the TEMA formula for the re-rate. On the data report (R-2 form), there is a space where you specify what edition/addenda the work is being performed to--this is where you document that the alteration is being performed using the edition/addenda of the original construction.
On the other hand, you may perform the re-rate using the latest edition/addenda of the ASME code. If you elect to re-rate using the latest edition/addenda, there have been some recent changes in ASME code (in addition to UHX tubesheets) that may cause some problems with the re-rate. ASME now requires that the pass partition rib area be considered when computing the required flange bolting.
Also, the flange rigidity requirements (formerly non-mandatory appendix S-1) have become a mandatory requirement of ASME code. These 2 new requirements may cause a problem if re-rating using the latest edition of ASME code.
Either way, it is important to understand that whichever edition/addenda you elect to choose, you must meet all requirements for that edition/addenda. You can't use some of the original and some of the latest.
Hope this helps,
Dan