e: I was thinking of installing CJB mods. Is there any single mod in it which is against the server's rules?
I use some of the mods from that pack, myself. So, I don't frown on using them. However, I doubt that you would be able to use the flying, teleporting, or item spawning mods (and more... I forget all of them in the pack) as you won't have "clearance" with Permissions benefit from them.
Like I've said before, I don't particularly care for client mods that can give an unfair advantage above other players. However, there is little that we can do to stop you from doing so. You'll just have to deal with whatever anti-cheat measures from the plugins that we have installed. ie, PX's flying/falling mishaps :V
Probably the only mod that I detest would be one like Too Many Items, or whatever could allow the player to spawn free items at will. First of all, that shit is lame and defeats the entire purpose of the game. Second, there are some items that just shouldn't be brought into a multiplayer game, as they could really piss people off or fuck stuff up. Spawn eggs come to mind.
Long story short, it's on you to decide which mods to try. The consequences are also yours to bear if the case arises. Tread carefully..

PS: Unless you dabble/get away with certain game-breaking mods that would piss others off, the most that you'd get from me is endless ridicule about modding in the first place. :V