Take a look on the ALIAS statement which provides a possibility to place a renaming before the load.
Quite practically is further just to store the new data-structure within a different folder and using a second load-statement for it. Yes, it creates some redundancy in the script but it keeps the logic simple.
Otherwise you would need some extra steps to identify the different structures per filename/filetime and/or pre-loading the header respectively first records to check which data exists and then to switch between various load-statements and/or to build one on-the-fly. It's no big magic but it increased the complexity and therefore it needs to be balanced which way is more expedient for you.
