May one use mezuzot with different scripts in the same house? For example can the mezuzah in one room be ashkenaz (beit yosef) and in another be sefardi (vellish)?
R Reuvain Mendlowitz in his book Inside stam answers the same question and writes
Ideally, all the mezuzos in one's home should be written according to one custom. Therefore, if one can afford it, the other kesav should be replaced.
In a footnote he quotes what he heard from his Rav, R Mordechai Friedlander (a well-known hilchot stam specialist) and R Shlomo Zalman Auerbach's Hilchot Shlomo 4:31
Halakhicly speaking it is fine. Since in the time of Hhazal there were no such cultural/ethnic divisions, no ruling (that I know of) was made on this matter.
Nor is this to be found in the earliest halakhic codifications (ie. Sepher Ha-Halakhoth of the RIF and Mishneh Torah of the RaMBaM)
It is also interesting as a side question as to what other ethnic groups like Mizrahim and Chabashim would do if they could not get mezuzoth according to their mesora and were faced with a "Ashkenazi or Sephardi" situation I assume they would take the irritating Israeli approach of "if their not from Ashkenaz their Sephardi" OR should they mix?