How can I do these things on my forums?

4 isn't possible without editing every $is_admmod check and a couple others
3 is possible by commenting out the checkbox and changing

$edited_sql = (!isset($_POST['silent']) || !$is_admmod) ? $edited_sql = ', edited='.time().', edited_by=\''.$db->escape($pun_user['username']).'\'' : '';

to

$edited_sql = ', edited='.time().', edited_by=\''.$db->escape($pun_user['username']).'\'';

2. Is possible through moderate.php, they delete like normal topics

1. Is very difficult

Nope, it's very simple. And very much needed. But that's an old debate...

For pogenwurst: look at the MarkAsRead modification. But it's a mod, so that mean ssh, svn, diff, patch, grep and all kind of dino-geeky-wizard things to keep your punbb updated after it (when it can be updated).

Now that I think about it, if you keep a "last edited" and "last edited post id" for each topic, you can check both: I was only thinking in terms of modding the code from what already existed.

Oh, and to explain #4 a little better
With a plain PunBB install, it's impossible to add another moderator group. However, if you edit the line in certain files for the variable $is_admmod (ie: edit.php, delete.php, viewforum.php, etc) so that another group matches it, you've "added" a group as moderators. You also have to make edits in profile.php so you can assign people in that user group to forums

"Sorry , but once again, I really can't say that I understand what you're saying."
You add 2 columns to the topic table in your database: last edited time, last edited ID. When a post is edited, you set them. When you go to viewforum.php, you have it check not only the last posted time (which it already does) but the last edited time as well

"Does that mod achieve the desired effect with editing posts that I mentioned before?"
No, it simply makes the topic read icons get marked more accurately

"Ok, I see what you're saying now. My PHP isn't that good, and I'm not that familiar with PunBB's source or inner workings or anything, but anyway could I do something along these lines?:"
Kind of
But if you did that, they would have moderation powers in all forums (including admin only forums!)

"If that's possible, is there a file in /include or something (common.php? - I dunno, just guessing by the name) to which I could add the code? Or would I just have to add it individually to each file where it's needed (assuming that would work, of course)"
Nope, it has to be manually edited in each file (of course, you could change it so that they all include 1 file, and have that 1 file have the is_admmod stuff).

erm, wtf is $cur_topic['edited']?
and why use OR? use ||
And that doesn't update the forum last posting info (on the index page)

Sorry, I meant why use it? He has it updating last_post anyway
and OR works, but for the sake of consistancy he should use ||

Thanks for your support Smartys, glad you appreciated my fix before crying at me, very positive attitude

I thought this mod would be welcomed better, but, anyway, I won't discuss more on that and here is the fix for the fix (fixing, coding, same thing isn't it? )

6 ) After modifications around line 126 (step 2) add:

                $errormessagestring='Post id='.$id.', Last poster='.$cur_post['poster'].' Forum id='.$fid;
                $db->query('UPDATE '.$db->prefix.'forums SET last_post='.time().', last_post_id='.$id.', last_poster=\''.$cur_post['poster'].'\' WHERE id='.$cur_post['fid']) or error('Unable to update forums. '.$errormessagestring, __FILE__, __LINE__, $db->error());

The edited message now appears in the main page of the forum as new. Happy foruming!