If you can show the VO that there are more opportunities in your home country for programmers (web development, mobile app, applications development, etc), you can easily justify the switch from systems to software. And with a prior background in systems, you can easily transition into the software development side (or what me and my classmates at Durham College call as the “dark side”). But be prepared for a lot of math as well in programming (some courses may require you to create a fully functional game as a final project).
So, your previous IT education is not a bachelor? The difference between a diploma and an advance diploma is that the former is a two year program while the later is a three year program.