Hey, I made an account just to reply to this. I'm a ET in the CG currently filling a MK-92 billet...big emphasis on currently. As a ET in the CG you're going to be required to fill a broad range of jobs within the electronics field. For your packet I would definitely emphasize that you are capable of learning technologies that you have never seen before. On the cutter I get my hands into a little of everything that's electronic (IFF, TACAN, SCCS, all of the radios, 73 radar, the small boat, 1MC, EVERYTHING!) even though I haven't had the C school and it isn't my billet. On shore I did small boat maintenance, DGPS, tower climbing/maintenance, and cutter support. You'll have to be a jack of all trades in the CG.
Since I've gone through a FC course (with a little info of the CIWS) I know how intense the systems are, so I know you can definitely learn it but I'd seriously make sure that you say that you know that CG ETs have a EXTREMELY broad knowledge base and that you're excited to take it on.
Best of luck and feel free to message me if you have any questions.