All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.
In principle, making a vow to perform a certain lawful act of devotion requires fulfilling it literally, because it becomes an obligation from the perspective of Sharia.
However, if the vow pertains to Udhiyah (Sacrifice), Aqiqah and the like, then it is permitted to change the sheep intended to be slaughtered with a better one; as stated by Shafie jurists(May Allah have mercy on their souls).
In this regard, Al-Imam Ash-Shirbini (May Allah have mercy on his soul) stated:" If a person vowed to slaughter a sheep and decided to slaughter a camel instead, then it avails since the latter is a better sacrifice.” [Moghni Al-Mohtaj vol.6 pp.250].
In conclusion, there is no harm on you (Asker) to slaughter the domestic sheep instead of the Romanian one. And Allah the Almighty knows best.