Yeah, I don't change my accent at all (weak Australian accent; same broad Commonwealth dialect as SA) during regular classes. Exposure to a broad range of accents is great, and the benefits are listed above over and over.
However, there is one exception here: just prior to the end of semester the MOE/POE issues standardised listening tests, especially at primary school level I'll fake it. Please, please go through and revise the TL with your students using either a set of American accented recordings or by faking one yourself on the relevant handful of words. You don't need to discuss the differences on a phonetic level or anything (and please refuse to answer the inevitable question of "which is better?" for the sake of the next guy) but just state there are two ways of saying this word (American and Commonwealth) so it is important they know both for the test, hint, hint.
If your MOE is anything like mine (Daejeon) they will find the absolute strongest, fastest American city accent they can find for the test, and churn out questions pivoting on the words "water", "tomato" and "class" again and again. Sometimes I feel there's actually a disproportionate amount of dialect specific questions on the tests compared to the curriculum and it... well... I almost start to feel like... nevermind. My personal paranoia aside, don't risk your kids failing because of your accent. Yes, it's only a handful of words at most (rhotic Rs, lazy flapped Ds and the old soft A before S rule) but these can pop up enough to ravage test scores if your students are not prepared.