Guru is called also an acarya
SB Canto 1
A guru is called also an ācārya, or a person who has personally assimilated all the essence of śāstras and has helped his disciples to adopt the ways.
SB 1.7.43, Purport: Arjuna arrested Asvatthama knowing perfectly well that he was the son of Dronacarya. Krsna also knew him to be so, but both of them condemned the murderer without consideration of his being the son of a brahmana. According to revealed scriptures, a teacher or spiritual master is liable to be rejected if he proves himself unworthy of the position of a guru or spiritual master. A guru is called also an acarya, or a person who has personally assimilated all the essence of sastras and has helped his disciples to adopt the ways. Asvatthama failed to discharge the duties of a brahmana or teacher, and therefore he was liable to be rejected from the exalted position of a brahmana.
So nobody can transgress the rules and regulation of śāstra, and what to speak of a guru. Guru is ācārya.
Lecture on SB 1.7.45-46 -- Vrndavana, October 5, 1976: If the guru is not in his proper way according to sastra... Guru means he must be abiding by the rules and regulation of the sastra. Sadhu-guru-sastra. Sadhu means one who is obeying the rules and regulation of sastra. Sastra must be the medium. Without sastra nothing is acceptable. That is spoken by Krsna. Tasmad sastra-vidhanoktah. Yah sastra-vidhim utsrjya vartate kama-karatah [Bg. 16.23]. So nobody can transgress the rules and regulation of sastra, and what to speak of a guru. Guru is acarya. Acinoti yah sastrani. One who knows the rules and regulation of the sastra and he teaches his disciple according to the sastra, he is called acarya. So acaryam mam vijaniyan navamanyeta karhicit [SB 11.17.27]. Acarya should be respected, as Krsna says, as good as Krsna.