However, we all know how unreliable manuscript traditions might be, and how extremely unreliable editions might be, especially if they are based on just a (few) manuscript(s).
An interesting example is the polemics about the first Indologists and their excessive audacy in emending texts, to which Patrick Olivelle dedicated vehement attacks in his Introduction to his edition of the Upaniṣads and in a 1998 article on the Journal of Indian Philosophy ("Unfaithful Transmitters", see here). Olivelle focusses especially on a passage of Chāndogya Upaniṣad (8.15.1), where Böhtlingk and, following him, Senart dared to add several words, because they could not make sense of the text. The text is in fact odd:
ācāryakulād vedam adhītya yathāvidhānaṃ guroḥ karmātiśeṣeṇa abhisamāvṛtya kuṭumbe śucau deśe svādhyāyam adhīyāno dhārmikān vidadhat |
The text apart from guroḥ karmātiśeṣeṇa means, at first sight:
After having studied the Veda according to the prescriptions, having returned from the teacher's home, reciting his own portion of the Veda in [one's] family, in a pure place, he should have virtuous sons.
But what could guroḥ karmātiśeṣeṇa mean? Böhtlingk in his Dictionary and in his edition of several Upaniṣads (1889a, 1889b, 1890a) postulated guroḥ karma kṛtvāviśeṣeṇa "after having performed an action for the teacher, in the undifferentiated [time]" (my translation, based on B's text). Senart followed him and even added sthitvā after kuṭumbe. Olivelle is quite against this "hubris" (his wording) in going against tradition. As partial apology of Böhtlingk, however, one might note that his first addition of kṛtvā is based on Śaṅkara's commentary (and hence, not only on his hubris):
guroḥ karma yatkartavyaṃ tatkṛtvā karmaśūnyo yo 'tiśiṣṭaḥ kālastena kālena vedamadhītyetyarthaḥ […] kuṭumbe sthitvā […]
Furthermore, I could finally understand the ChUp's wording through a later article of Böhtlingk (1897a Bemerkungen zu einigen Upanishaden BKSGW, available on Archives.org, see here), where he goes back to the traditional reading and refers to Gautama Dharmasūtra 3.6: guroḥ karmaśeṣena japet. This Dharmasūtra does not add any further word and, therefore, it makes clear that guroḥ karmaśeṣa (and possibly karmātiśeṣa) had a fixed conventional meaning, possibly "the [time] remaing out of having performed one's duties towards one's teacher". It is also noteworthy that karmaśeṣa is a sāpekṣasamāsa, which needs to be connected with guroḥ.
What is your policy? When did you end up emending a text?
On my general policy, favouring the text over me as a reader, see No. 6 in this post.