Hi Mandy (or do you prefer Amanda?),
Thanks for posting this! I've added a few thoughts below. As always, before adding my comments, I'll give my standard disclaimer that I'm trying to be as direct as possible because this is the time where you can't have a misstep. So, if it ever sounds harsh (I hope not), just know it isn't meant that way—I'm trying to help you produce the best possible application
Ok, that said, I'm not totally sold that this addendum is necessary, but if you do submit it, I would suggest several changes.
First, there are so many details in the opening paragraph that I think you lose the reader. It's hard to see the big picture when it's obscured behind so much information. Fortunately, I don't think most of it is necessary. For example, the exact jobs you held won't make a difference to the committee; knowing that it was two jobs during school is enough. Consequently, I think you can safely delete every parenthetical in the entire statement.
Second, the second paragraph seems less fluent than the first, and has a choppier feel. I understand what you are doing here in regard to the major switch, but I would lead with more of a discussion of changing majors as opposed to that only being clear midway through the paragraph.
Last, and perhaps most importantly, I think you need a clearer statement that your current GPA (around 3.55 probably?) isn't representative. That information is in here, but I feel like you make the reader draw the conclusion about what you are saying, as opposed to making it clear up front (and that's what you need to do since they don't have a lot of time for these; yes, your GPA is on your records but you never want them to have to search for another piece of paper if you can avoid it). An addendum requires a certain degree of directness and clarity that isn't always needed in a personal statement. You want the reader to walk away saying, "Hmm, that made a lot of sense. I see why that isn't a big deal now."
As I said before, I'm not sold that this is needed, but in an improved form it probably wouldn't hurt your chances. So, if you felt it was needed, I wouldn't object
I hope that helps. Thanks!