What is the policy of this forum toward these individuals?
I think the policy has been to tolerate or welcome such a statement.
Consider this interchange from 2015 (in which Sankha is Theravada, and Andrei Mahayana):
- Theravada Buddhists don't really recognize other schools. Mostly historians do that. So it's just Buddhism for us. – Sankha Kulathantille
- And we do recognize other schools, it's all Buddhism for us :) – Andrei Volkov♦
One of the reasons I find it easy to tolerate is that Sankha says such a thing only when he's prompted to, by other people commenting on his answers: e.g. here the 'provocation' is Lanka telling him to say that his answer is "based in Theravada Buddhism", and here it was you saying, "Theravada Buddhism is just one school of Buddhism; it is not Buddhism".
If you're allowed to define what Buddhism is, I think Sankha is too!
Such a comment might easily be seen as hostile, if he were to go out of this way to post it under someone else's answer, but he doesn't: it's an explanation of his own answer.
Actually I find it admirable (and helpful): explaining his own perspective, without attacking other people's answers.
As moderator I will generally sympathise with the author of an answer. If the author of an answer flags a comment (as hostile or not constructive) then I'm inclined to delete the comment. Thus you can post answers, and I'll help to protect your answers and end any unwanted arguments about them. Similarly Sankha is welcome to post answers too.
One of the things that avoids "verbal guerilla warfare" is the emphasis on Q&A, i.e. the emphasis on people writing their own answers. You can ask use comments to ask people to clarify their answers, but comments may be deleted if they don't improve the answer.
Generally it's the author of each answer who's allowed the last word.
consistently answer questions that are not about Theravada from a Theravadin perspective
The convention we've established on this site is to use school-specific tags. For example if you use a school-specific tag (mahayana, zen, vajrayana, tibetan-buddhism, secular-buddhism, etc.) then only answers from that school are on-topic.
Using such a tag might signal that you don't want Theravada answers to your question.
It might be unusual to do that, though, when you're asking a question about Pali texts. Given that you are asking about Pali texts I think it's easy to see how someone might think you were interested in a Theravada perspective.
If you don't use such a tag, that's a signal you're inviting answers from any/all schools.
I hope this meta-answer helps. I suppose that a purpose of using tags is to let people post questions without getting hostile answers, and moderating comments is to let people post answers without getting hostile comments.