Blacklist explosives and beakers from the teleporter without emagging it.

[zjdtmkhzt]

tbh, I don't really like this. Blob nuclei are already teleblocked, I believe, and nukies are mobile, so they can just walk around and be difficult to accurately hit. Also, teleporting explosives at the nuke has a high chance of also hitting other crew instead, so a normal crewmember usually can't do it anyway.
Plus, if you really think it'll be a problem, you can always send someone to blow up the mainframe.

In addition, the emag really already does plenty of things.