Nothing specific from RFU on that topic that I am aware of, but we handle it at Society level in our training programmes, especially for newer refs.
Our members are given clear guidance in a Society wide session as to what are the typical criteria bands for a b*llocking, a YC and as RC. But as we all know there are grrey areas and each incident is of course taken on its own merit, based on game context, management challenges, previous behaviours of teams and individuals, and what actually happened, what the referee saw, and their judgement (based on rugby experience).
We have role play sessions for new refs on how to deal with confrontation generally (often using police or services personnel as our experts based on their training), and we show some best practice videos (Wayne, St Nigel, etc). We cover techniques for control - separating the teams, getting AR input (where appointed), calming the situation generally, backing away to make the offenders come to you with their skippers, deal with full on brawl combatants separately (or risk having it re-start in front of you, assertive body langauge and wording, how to avoid a debate ("I am talking, you are listening"), ow to word the actual boll*cking (dont paint yourself into a corner) or YC/RC dismissal and correct show of the card with clear reasons stated for it.
Also the techniques used are different depending on the personality, character and communication skills of each referee - we are not robots !