Hey, i have a related question about this:

I have an old iPhone that has all my old Signal messages still on it that I wasnt able to move with me when I switched to Android. Is there any way that I can use these new tools to move the old conversations on my iPhone over to my android phone without losing all the new messages that are on my android now?

That is, I want to merge the two histories.

Using the new backup feature that we're discussing here (once it is available on iOS), you will probably need to transfer your old iPhone's data to an Android device first (either a secondary one or your current one, provided you have backed up its data to a backup file). Then follow https://news.ycombinator.com/item?id=45174779 .

Unfortunately we don't have immediate plans to support merging of histories. As others have noted, you may be able to use third-party tools to merge them together, but that's very much a "at your own risk" sort of thing :)