I agree that the final consonant before a repetition should be omitted, and I think that using brackets as you have proposed will work well.
I agree that one should follow the standard method of writing English lyrics for music in Western notation, as you have proposed. But I am not so sure about putting the final consonant in parentheses if it continues for more than one line of music, mostly because it just looks messy. If you feel the need to remind the singer which consonant to sing after holding out a vowel for a long time, you should do so not only at the end of a word, but at any point in the word. For example, while singing "mys - - - - - - tic - - - [linebreak] - - - - - - - al" it would be easy to forget which consonant to sing after the linebreak. By the same logic, a reminder could be placed, like so: "mys - - - - - - tic - - - [linebreak] - - - - - - - (c)al." But I still think that such reminders look messy. In other words, I might pencil in a reminder like that in a score if I was making a mistake often, but I wouldn't want the published score to have reminders at every instance.
I will comment on the meaningless consonant "n" in the other thread you have started.