This is something we addressed internally by giving a list of variables in the side bar of the editor. It was made visible to employees because at the time, none of the moderator-editable pages contained any of these variables, or at least we were pretty sure they didn't.
That's not the case now (obviously), however I believe $SiteName is the only one you'd have to contend with as a mod unless circumstances on your site made making additional pages in the help center mod-editable. This is unlikely, but not impossible to happen, so I'm dumping the list here for the sake of institutional memory:
MetaUrl: The URL to the per-site meta
SiteName: The Name Of The Site
SiteShortName: The short (canonical or botique) name of the site
CurrentTier: Production Or Development
TeamEmail: The email address support requests sent from this site go
Topic: The site topic
Year: The year the site was created
SiteImagePath/: Relative path where images are stored
Audience: Who is this site for?
ChatUrl: Chat URL for this site
BaseWebsiteAddressBare: The base address of the site (no http(s)://)
BaseWebsiteAddress: The base address of the site (with http(s)://)
CommunityLeaderName: Currently Robert Cartaino (used in email)
CommunityLeaderEmail: The email address of the CommunityLeader (currently Robert's)
Privilege-ModerationTools: Rep required for moderation tools
Privilege-CloseQuestion: Rep required to close questions
Privilege-PostEditing: Rep required to directly edit posts
Privilege-EstablishedUser: Established user reputation threshold
Privilege-CloseOwnQuestion: Rep needed to close, or see close votes on your own questions
Privilege-PostCommenting: Rep needed to comment
Privilege-CommunityPostEditing: Rep needed to edit community wiki posts
Privilege-TagEditing: Rep needed to re-tag questions
Privilege-ReducedAds: Rep needed to reduce ads
Privilege-CreateNewTags: Rep needed to create new tags
Privilege-VoteDownMod: Rep needed to down-vote
Privilege-Bounty: Rep needed to offer a bounty
Privilege-VoteUpMod: Rep needed to up-vote
Privilege-VoteOffensive: Rep needed to flag as offensive
Privilege-Newbie: Rep needed to remove new user restrictions
Privilege-CreatePost: Rep needed to post a question or answer
Privilege-TrustedUser: Rep threshold to become a trusted user
Privilege-SuggestTagSynonym: Rep needed to suggest tag synonyms
Privilege-ParticipateInMeta: Rep needed to post on a child meta site
Privilege-CommunityWiki: Rep needed to apply community wiki status to your own posts
Privilege-Chat: Rep needed to talk in chat
Privilege-ChatRoom: Rep needed to create a chat room
Privilege-GalleryChatRoom: Rep needed to create a gallery chat room
Privilege-ProtectQuestions: Rep needed to protect a question
Privilege-ApproveTagWikiEdits: Rep needed to approve tag wiki edits
ReputationRequiredToClose: Rep needed to close questions
CloseVotesPerDay: The number of close votes users have in a day
VotesNeededForClosure: The number of votes needed to close a question
Questions.Bounty.DurationInDays: The duration (in days) that bounties run
You should not need most of these. Rep thresholds are only variables because we can and (very infrequently) do slightly adjust the levels that certain privileges are unlocked on certain sites. The rest is pretty self-explanatory.
I'm going to re-visit this and see if I can just get the help turned on for mods too, even if only a few of the variables would be of any practical use to you.
Sowwy about 'dat! Pretty sure I derped when I said 'mods shouldn't need this'. It's not that they're seekrit or something, it's just that we like to keep the amount of clutter that we push at you minimized whenever possible.