Jewish liturgy is fairly consistent across geographic traditions but even small differences matter when selecting a permanent text for a specific synagogue. For example, the Kaddish prayer is universally recited at many places in the service but a few words differ between the Ashkenazic, Middle Eastern and pseudo-Sephardic (Chassidic) texts. Repetition breeds familiarity and comfort, or constant irritation for those who prefer a different text.
When a synagogue’s demographics change, can its official text change as well? This is an emotionally charged issue that is best decided by rules rather than by the subjective determination of a rabbi bound to offend many congregants by selecting one side. R. Yerachmiel Fried, in his Yom Tov Sheini Ke-Hilkhaso (final chapter, par. 16), settles the issue as follows:
A synagogue whose founders established its text as Nusach Ashkenaz according to the agreement of a majority of members, and through the years new members joined, even though the majority now wants to pray in Nusach Sefard the synagogue may not change its text because there are still many members who wish to continue praying Nusach Ashkenaz, even though they are now the minority. The same applies in reverse.
All this only applies if they want to change a prayer practice in a way that contradicts their previous practice… But if they… only want to add to previous practices… they may change with majority agreement.  Mishnah Berurah 68:4. And see Responsa Yaskil Avdi 7:8. This also applies to a private synagogue; see Responsa Zikhron Yehudah no. 46; and see Pischei Teshuvah, Orach Chaim regarding a synagogue with no established “format”.
 Iggeros Moshe, Orach Chaim vol. 2 no. 21. And see Bi’ur Halakhah 468 sv. ve-chumrei ha-makom; Responsa Maharshdam, Orach Chaim no. 35; Chelkas Ya’akov, Orach Chaim no. 79 regarding a synagogue built by a donor on condition it prays a specific “format”, under what conditions may it change. And also see on these matter Mishnas Yosef (by R. Lieberman), Hilkhos Beis Ha-Kenesses.