HET vs Astrophysics Undergrad Research

I've heard that some grad schools want you to know which subfield you want to go into when you apply. I want to do HET, but I'm afraid I won't be a competitive applicant. I am going into my junior year and I need to decide which area to do research in (because I'm told I need to start specializing in my last two years). Should I do research in something less competitive (astrophysics maybe?) and then put that as my preferred subfield to increase my chances of getting into a good school (switching fields after getting in), or should I do HET research anyway and then say I want to probably do a different area of physics (which, given the jumping around I've done, will probably be plausible to someone reading my application)? Or should I do something entirely different strategically?