You’re making this much too complicated. Think of it this way. Every transferable class you’ve taken will be used in determining what requirements you’ve satisfied towards UC graduation. Some count as general ed, some as major prereq, some for your major. This is always true, no matter how many transferable units you have.
Then they look at the total number of units you are bringing in. Less than 70 semester units? Great, all the units count towards the unit count needed for UC graduation. More than 70 units? They only let you have 70 units towards the 120 you need for a UC degree.
What have you done differently in deciding engineering is right for you that you didn’t do when picking accounting? “Engineering” sounds kinda vague, you’ll need to pick a specific branch when you apply to xfer. I hope I’m wrong, but this sounds a lot like the kids that were saying “I want to go into law” a few years ago because they thought it would lead to a high paying job, the details of what type of lawyer to be figured out later, the assumption being that of course they’d be fine with it as a career.