I've performed integration (p4 integrate) and then resolved conflicts in all files (p4 resolve ...). After that I noticed that one conflict could be resolved better by providing additional edits.
I want Perforce to think that the additional edits (after p4 edit file/in/question and vim file/in/question) are part of resolution, not an separate edit.
How can achieve this using p4 command line tool?
If you do p4 edit and make the edits, they will be part of the same atomic changelist and the same revision.
(It is possible to make the edits in such a way as to have them not get propagated back to the source on a reverse integrate, by "hiding" them in the merge, but you probably don't want to do this because it likely means you'll end up re-resolving the conflict later.)