There are a lot of other people here that have, for the most part, summed up what I am thinking. For this reason, I will not restate their information. With this being said, I think you need to heed other peoples warnings and take it to heart. While I don't mean to discourage you, the fact of the matter is this: you need to reevaluate you current goals. You say that you want to modify a game engine (that you did not code and have no knowledge of), going on to state that you have no knowledge of C++. Plain and simple -- this is not going to happen. It takes many man hours and huge teams of people to achieve what you are wanting to achieve. I have 8+ years coding with C++; before that, I had several years of low-level C coding. I (as well as most other programmers) work for 10+ hours a day. At this rate (in a team), it would still take years to achieve what you are wanting to do. Adding to the point of not knowing C++, you state that it won't take you years to learn C++, only a couple of months. I don't know a single programmer (including myself) that is still not learning their language a decade after they started.
With that out of the way, I will offer you this advice. You hint at the fact that you know how to program in another language. I assume that your goal is to make a game. My advice to you is move into mobile development. This will teach you some things that can be applied to other languages, it can be done with a smaller number of man hours, and there is money to be made. After you spend some time there, then move on to smaller projects.