1st - CHange the description of a savegame? Sort of - if you overwrite the slot with a new saved game with a new description... but I think that's all you can do.
2nd - I don't have access to the manual right now, but check out whatever has replaced the StrFormat() function and use it to create the string you need for "output.WriteString".
3 - From what I understand, it goes like this: open a file and call five WrtiteStrings and 5 will be created -. let's call them 1 to 5. Then close it and call ReadStrings 5 times - the five will be called, in the same order. Andf if you wanted to, say, read the fourth string, you'd call ReadString 4 times, always overwriting the previous one. I THINK this is how it works... bit of a hassle IMHO but not a major one, and it works.