Hi
Fervids77,
Thank you for your question. Congratulations on the new opportunity. I recommend that you update the admissions committee about the new job when the time comes. You can send an email with a few sentences explaining why you made the change, that it represents a de facto promotion, how it continues to build toward your MBA subsequent career goals (and in what way... think new knowledge, skills, experience, responsibility), and how you believe that working there for about a year prior to enrolling in the MBA program will still be positive and beneficial. Include your Application ID number in the email. And you might consider attaching an updated resume (PDF) to the email as well. There probably won't be too much new content from new job, but it will help solidify and professionalize the change.
It's a little jumpy to change during application season, but it happens, so just be able to explain your rationale and highlight what you believe are the benefits (advancement in your pre- and post-MBA industry, etc.) in the aforementioned update email and in the interview(s) down the line. You'll end up being there for less than a year if you get into these MBA programs, but it can still come across as a positive for your applications (again, given the "advancement") if explained properly.
The other question is when to send the update. If you lack career advancement, you might even aim to send the update soon after you apply, that way it's part of what they review when deciding whether to grant you an application. Or you could indicate or explain the coming transition when you apply in the first place. That decision would be strategic and would have to be made in context of the specific timing of the transition and strengths and weaknesses of your candidacy.
Best Regards,
Greg