206 is on the thick side for 1.5-mil tape. Are you planning to record material over the splice? If not I think it should be ok. You might hear a pop depending on the machine, angle and quality of the splice.
Use good splicing practices... demag your razor, etc.
A trick when going from one thickness to another is to put a short piece of splicing tape on the back of the thinner tape to make it thicker at the joint. Carefully place the splicing tape on the thinner audiotape and then cut it so ends are even. Now, just splice as usual in the block with a second length of tape.
~Tim