I know that diacritics are often retained in loanwords in formal writing (cf. naïveté), but I haven't seen this done with direct adaptation of Latin words; i.e., per se.
In Latin, per sē comes with a macron, indicating the longness of the vowel. This practice is uncommon (unused?) in English, but so are accents and diæresis marks, which are retained in the aforementioned naïveté.
Is there any attested usage or relevant guideline regarding the adaptation of macrons from Latin?