I am predicating this on two ideas:
- That a person can be obligated now to bring a korban in the future, the way a convert today will be required to bring a korban when moshiach comes.
- A Nazir brings a chatas to atone for his having made something allowed to him by Hashem, forbidden to him.
The Gemara (Nedarim 10a) also questions why the nazir must offer a korban chatas, and it answers that the sin he committed was his original decision to needlessly cause himself suffering by abstaining from wine. After the Gemara states clearly that voluntarily refraining from physical enjoyment is considered sinful...
from Nedarim 10a
ומה זה שלא ציער עצמו אלא מן היין נקרא חוטא המצער עצמו מכל דבר, על אחת כמה וכמה מכאן כל היושב בתענית נקרא חוטא
If so, does our behavior outside of Israel, refraining from melacha (the lack of which which might cause tza'ar moreso than just not drinking wine) on a day which is not a holiday (because we hold Yom Tov Sheini Shel Galuyos), obligate us in the future to a korban chatas? Is this self-imposed stricture similar to the vow a Nazir takes? In fact, do the various "syags", the gezeirot/takanot and fences enacted rabbinically which stop me from doing something which might be allowed textually all rise to that same level and would all obligate me to a future chatas?