I got in as a Mechanical Engineer. I was contemplating between MechE and EECS when I applied and I ended up doing MechE because it’s broader and also a bit easier to get in than EECS. I don’t plan on doing so, but if I change my mind, how hard would it be to change from MechE to EECS? Are there only certain requirements to fulfill and a GPA to maintain or do they evaluate you holistically if there are others competing with you to switch into EECS as well with the same GPA and requirements fulfilled? I got in as a regent scholar if that makes a difference. They give priority enrollment for classes 
would they give me the same priority consideration with major changes if too many apply for a change into EECS with similar GPAs?
When I went to ROHP, my host was intending on switching from BioE to EECS. She said as long as you maintain the right GPA and complete a year at Berkeley with your current major, it’s easy to switch within CoE.
http://engineering.berkeley.edu/academics/majors-minors/change-major
http://engineering.berkeley.edu/academics/undergraduate-guide/degree-requirements-and-major-information
http://engineering.berkeley.edu/admissions/undergrad-admissions/prospective-freshman-faqs
The last link indicates that EECS and BioE are more impacted and difficult to change into.
In general, keeping up a 3.0 and performing well in the intro classes of the new department are all that matters.
Anecdotally, I had a friend who switched from Mech E to EECS. The department told him to finish CS 61A/61B/61C/70 and EE 20/40 (now EE 16A/16B) with a strong (he got a 3.5 or so iirc) GPA, and maintain a 3.0 overall. He did both and was successful in switching.
Most people I know who switched engineering majors did so after their third semester, some did after their second or fourth.
So if I intend to switch to EECS, do I basically take the exact same freshman courses as other EECS majors and do good in them? (3.5+ gpa) and then apply for the switch after the 1st year? What if I don’t get a good gpa and my app to switch doesnt get approved, would I have “wasted” my first year? (by wasted I mean taken unnecessary classes for my MechE major and therefore wasted time).
Yes, you will have to either take both majors’ courses, or prioritize one over the other, but that could mean “wasting” some of the schedule space on courses that you would otherwise not have taken.
It does say minimum of one semester, although there may be department requirements that require more semesters. You may want to ask the EECS department directly if you cannot find what you need on the web.