I'm familiar with child themes for Magento and the fallback mechanism Magento utilises, but I am not familiar with how the local.xml file works.
The other day I asked a question on here and the answer was to add to the local.xml file. See here: How to add a block at the very top of every page?
Now, I did that with success but since then I have upgraded my Magento version to 1.9.1 and have just realised that my changes have now gone from the local.xml file.
How do you modify the local.xml file so that it won't revert back when you upgrade Magento versions?
Does it work in the same manner as themes, where you can create a copy of the local.xml file and place it in the child directory?