Wood – How to vertically connect two 4x4s on a deck to build a roof

They make a metal brack to span the old 2X4 and you most likely can get it to work for the new roof. If not I can most likely get some made at work. You do have some good bracing and support on the one footing you have pictured here and if the other one is the same way it would be just as strong.

I would just pull out the old footings and replace them with the new style footing and be done with it.

Reasons: 1) you would always have questions as to how strong the modified brackets (ie the roof/posts are) and 2) By replaceing the old footing /posts you now have done the job and will pass and inspector.

Burying the wood post will cause it to rot prematurely. Even ground-contact rated Pressure Treated lumber won't last forever.

The only benefit of burying the post (besides it being easier to do) is lateral stability. i.e. you can sometimes neglect lateral bracing this way.

Best practice for wood-post decks is to have the concrete extend above grade and use a stand-off post anchor to hold the wood post to concrete.

Here is an example of this with some knee-braces for lateral bracing. The braces don't match so I find this somewhat ugly, but the image is clear and easy to understand.

Footings here don't need to be deep so I often form my own square ones but sometimes I use bigfoot forms and I really like those. Although Shirlock's "mushroom" method is more than adequate if you are only required 8" wide.