Third,if you transfer, then it is also a new environment where you should start all over again, new friends, new housing situation, and new teachers. That must be tough. And most likely you will go to a college somewhere else again one year later. The first semester at senior year is the busiest time for you to create applications, to take tests, and to maintain good grades for colleges as well. In this situation, adding another pressure to you such as adjusting to a new environment would not be very practical unless you have some exceptional reasons.
I suggest you rather to take good college counseling and guidance while staying at the current school and that will possibly bring a better result to you.
Transferring to another school as a senior is usually not recommended. There are a few reasons why. First, as you mentioned, there are not so many schools that allow this type of transfer. Honestly, schools would possibly see that you would want to receive a high school diploma after just a year of stay and that does not sound good to them. Schools care more about students' growth as they become valuable part of their communities throughout entire school years. Secondly from college counseling point of view, this transfer does not any give positive view on you either, unless you present exceptional reasons why you transferred to a particular school at the senior year, and still this makes college admission office wonder why you did. Also, most elements of college application preparation will be done by your junior year; your transcript in junior year will be more important than that in senior year and your activities until junior year will be considered more as colleges review your file.