But you should also have access to /cmd versions of the game in case you don't have the GUIs.
and a bloody help article system because i can't find out how to do some things GOD DANG IT
There is access to /cmd because they use serverCmds, just like /cmds.
However. Please tell me when it's reasonable to use /cmds to utilize 30 inventory slots with stackable item counts, 11 equipment slots, shops, and stats (exp and level) for 10 different skills.
The trouble is every Add-On wanting a GUI keybinded to your keyboard. There's a limit to human memory of so many keybinds for so many GUIs you'll barely get use of. Also, most RPGs in Blockland work without clientside downloads. I've only found a few cases, and it is annoying to get locked out of servers by it. I have this one GUI, have no idea what it is, and it seems useless to me. I will delete it, as it is just a random keybind whereas I must manually click the X to close.
It would be cool if Blockland had some default blank overlay that you could stick all the add-on GUIs in.
My point is, if every mod makes that excuse, we'll have a stuffstorm of random GUIs with barely any use that you MUST have to play 10% of servers that use just that individual one, let alone the others that take up other percentages.
If you stop playing in a server that uses a certain client add-on, delete it.
If you happen to play in multiple servers that use different add-ons, which I guarantee you that you don't play in more than 4 of, either make multiple copies (hell, even make them instantly join a certain ip), or just deal with the fact that you'll have key combinations for 4 different guis (which isn't hard to manage). Please remember that you can use modifier keys plus any key, such as shift+q, as I used for DRPG.
If you're playing in more than 4 different servers that require GUIs, then maybe you should slow down.
If you're playing in more than 4 different servers that require GUIs because they close often for long periods of time, then they aren't worth playing in.
Besides. I can only think of 3 mods that require use of a GUI. (Things like TDM and zombies don't count because you're not using keybinds and only the server actually needs it)
DRPG.
One City RPG server.
Rise of Blockland (it's closed)
The rest that require keybinds are not for gamemodes, such as RTB, Compass, and whatever. But those help you on all servers, not just for one.
tl;dr
If you don't want the GUI, don't play on the server.
Because other people don't seem to have a problem using the GUI.
Oh and about the whole virus thing. If it were possible then someone would've done it by now. No one has done it. If you want to prove that you can then please do.
As to answer
Brolaf Olaf's question. Sorry, this actually isn't possible.
The most you can do is remind them to, and instruct them how to do so.