If you can give us perhaps 5-10 items with data that you're working with (you can always edit out any personal information if you don't want us to see it), we can probably offer better options (including how you might be able to swap data with item names, even after it was already added to the hash table. The initial swapping may take a good amount of time on a large table, but afterwards wouldn't be needed at all since you can change the saving of data to use the new format.
Oh, although using "/hsave -i" will corrupt item names that have 's, that's only a problem if you have item names that will have 's. If you don't, that's not an issue. I'm unsure about the INI size limit for /hload. Variables are loaded fine over the 64k limit, but $readini can't... so, it's possible that /hload may or may not be able to load past that 64k limit. Only way to know is to test.