The challenge with trying to just use the append tool is that you're typically going to have to do a fair amount of translation to get from your current model to the target model. This means that if you want to use GP tools to accomplish this you will likely need to go through several iterations of deriving new feature classes that slice and dice your data in different ways, along with translating values between the source and target domains.
If you have the data interop license available I'd recommend you check out the sample workbenches Esri has provided that allow you to do these operations using FME / Data Interop.
Because you're an Electric client you'll also need to consider how you're going to handle the fidelity of your data, and you may need to also introduce code to handle the creation of any additional connection points or terminals you need.
If this seems like its too much work Esri has a large network of partners and a Utility Network specialty program specifically designed to get you in touch with a company who can help talk you through the process or do some / all the work for you.
