The general rule is to handle emendations, information about placement etc. as you would handle variant readings from a second manuscript. A lot depends on whether you are talking about one footnote, an appendix, or the main text. I don't know of a guide. Probably, you want to look at a number of editions, decide what it best suited to the material you are dealing with, and follow the conventions adopted by that editor.
Parkes is a good suggestion.
But you will want to follow the conventions of someone active in your speciality.