I would like to know if it is possible to write and submit a comment/reply to an article that has been published earlier (by oneself). This is because there are new results that underline the findings and conclusions of the previous article that havent been published yet and are not enough material for a seperate publication. Would this be appropriate or are comments from the same authors not wished for by the editors of the journal?
Don't write a comment on your earlier paper. Write a short article and post it on a pre-print server, or submit it to an open-access journal, depending on your field.
Don't do it. Comments are specifically meant as critiques of (possible) problems with published articles. They are not appropriate as ways to elaborate on your own research.