When we made aliyah, I spoke to the Rav of our new shule at length about changing nusach and pronunciation. (All the shules on our yishuv are nusach Sfard, while in America I davened Askanaz.) He told me it was OK to switch nusach, but not to switch pronunciation to Sfardit. His reasoning was that most people who do so end up pronouncing the words incorrectly. Since the shule has no rules about having to daven Sfardit when davening for the amud, I stuck with my own pronunciation.
