Specifying different compression ratios for different types and/or specifying them for diff archives creation, neither one possible?

[Byt3]

I'm trying to use my 7z for backups.
Is there a way to do any of the following :

1. Specify different compression methods and ratios for different file types / extensions.

2. Use -u- Diff archive method and specify file extensions that will be updated.

3. I couldn't do neither of the above
   so tried updating the diff, but I get a
   "file already exists" error so cannot even do several passes to get it done.

4. UsIng -ir To try to get Only File extensions specified exclusively doesn't work with the diff method.

Thanks for any help you can offer me on this.