Can you derive benefit from other Jews' melachas during an extension of Shabbos?

Question

My question refers to the practice of tosafos Shabbos, or extending the duration of Shabbos. In Yoma 81b this is called a mitzvah, and we learn one is required to do so at both the beginning and the end of Shabbos--but one only needs to do it by very short times, which are probably already reflected in the published z'manim. However, I have heard in a few places that very pious people may extend the Shabbos even longer, and that this is considered meritorious.

My question is this: if one is deliberately extending one's Shabbos, and others are not, is it halachically acceptable to derive benefit from melachos they are doing during your extension? On one hand, they are not doing the melachas in violation of Shabbos--but on the other hand, shouldn't your observance stay exactly the same throughout your Shabbos?

This probably connects to the question of whether you can derive benefit from the melacha of a Jew in another part of the world for whom it is not Shabbos...

Answer 1

The Shulchan Aruch of R' Shneur Zalman of Liadi (263:25) writes:

מי שקדם להתפלל ערבית של שבת קודם שהתפללו הקהל אף על פי שכבר חל עליו קבלת שבת יכול לומר אפילו לישראל חבירו שלא קבל עדיין השבת שיעשה לו מלאכה ומותר לו ליהנות מהמלאכה בשבת דכיון (ח) שלחבירו מותר הוא אין באמירתו אליו איסור כלל(ולא אסרו האמירה לנכרי אף על פי שאינו מצווה על השבת) אלא כשאומר לו בשעה האסורה לכל ישראל (עיין סי' רס"א).

וכן מי שמאחר להתפלל ערבית במוצאי שבת או שממשיך סעודתו בלילה מותר לו לומר אפילו לישראל שכבר התפלל והבדיל בתפלה שיעשה לו מלאכה ומותר לו ליהנות ולאכול ממלאכתו אע"פ שאח"כ יזכיר עדיין של שבת בברכת המזון:

One who prayed Friday night Maariv before the community, even though he already accepted Shabbos, can tell another Jew who didn't accept Shabbos to do work for him and he can benefit from the work. The reason is that since his friend is permitted to do work then, there is no prohibition of telling him to do work then. ([This is not similar] to telling a non-Jew to do work even though he's not commanded to keep Shabbos) [since it's only forbidden to tell a non-Jew to do work] when it's forbidden for all Jews.

So too, if one is late at praying after Shabbos or he continues his meal after Shabbos one is allowed to tell a Jew who already prayed [Maariv] and did Havdala in his prayer to do work for him and to eat of his work even though he will mention afterwards mention Shabbos in benching.