Can someone, who has not yet taken on Shabbos, recite the Friday night kiddush (before sunset) for someone else who has already taken on Shabbos, [without the former intending to take on Shabbos with the kiddush]?
With Hashem's help I just found that R' Akiva Eiger in his commentary on Shulchan Aruch (OC 267:1 - או"ח רסו ס"ק א) asks this exact question, and he remains in doubt.
"מסתפקנא אם אחר שלא קבל עליו שבת יכול להוציא לקדש למי שקבל עליו שבת, די"ל דלזה שלא קבל דהוא חול אצלו הוי כאינו מחוייב בדבר, כההיא דירושלמי הובא בתוספות יבמות דף י"ד בן עיר אינו יכול להוציא לבן כרך דהוי אינו מחוייב בדבר, או דהכא עדיף דבידו להביא עצמו לידי חיוב לקבל עליו שבת, וצ"ע לדינא":
It is questionable whether one who has not yet taken on Shabbos may be motzi with kiddush someone who has already taken on Shabbos. One may say, that the one who has not yet taken on Shabbos is considered as "having no obligation for this thing", similar to that which is stated in Yerushalmi, which is brought in the Tosfos (Yevamos 14) A "city" person, [a resident of an unwalled town, where the Megilla is read on the fourteenth of Adar], cannot be motzi [with the reading of the Megillah on the 15th of Adar] a "metropolis" person, [a resident of a walled city, where the Megilla is read on the fifteenth of Adar], since he (the reader) is one who is not obligated for that. Or [we might say] here [in the case of kiddush] it may be better since he can bring himself to become obligated by taking on Shabbos. Vetzarich iyun. [concentrated study is needed to decide the law].
No, because reciting the Bracha is automatically performing the Mitzvah and therefore automatically accepting Shabbos. The better question is the other way around -- can someone who accepted Shabbos make kiddush for someone who has not (2nd person) and can that 2nd person still do Melacha (until a few minutes befor sunset)?