I think you will need to at least rewrite each directory in your TIFFs. But please make sure the library writes relevant tags with the data type you need (or change the source code of the library if it doesn't).
In case X9.37 files (I don't know what it is) require TIFF directory to be placed in certain places of the file, you might be forced to recreate the file completely (by copying tags and raw raster).