What is the antonym of "update"?

Question

For similar words, the antonym is obtained by simply substitute the substring up with down like in the following:

• upgrade - downgrade
• upload - download

What about update? I searched for something like downdate but it has very few occurrences and I'm not sure if it is only a rare used word or a wrong one.

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A bit of context

The use is related to computer specific context. If I think of update's meaning as up-to-the-current-date, then the word that I need to use should have the meaning of up-to-the-past-date. As suggested in an answer, good candidates can be rollback, reverting and restoring. However, all of them suggest the idea of modify something in order to make it equal to a past state. In my case it's a bit different. It's a chunk of code that works well with current version of some programming language API but since it needs to be run with an older version I modified it to be compatible with this older version. Maybe in this case I could just say 'updated to the previous API version' but I wonder if the use of downdate is correct.

Answer 1

If it is reversing a process [particularly computer-related updates], I think the closest word is "rollback" or "reverting" to the previous version or idea. Windows systems have system "restore".

In the context of the state of being updated (i.e., up-to-date), then it's "obsolete" or "out-of-date".

I believe there are other possible answers.

Answer 2

There is no "downdate" in those few dictionaries I checked. People sometimes use it to suggest someone to change a current version of a program to an older version, but this is not what you are asking.

So, you may want to use modify or one of its synonyms: adapt, convert, customize, tweak...or, simply, make compatible.