Everybody is super nervous about possible hiccups or, goodness forbid, failure modes of the telescope. It is a fairly complicated machine.
The telescope will be at the second Lagrange point, several light seconds away from Earth, about five times as far as the Moon. But then L2 is not a gravity well so that no descend vehicle is needed; all that is needed is a launch system and a spacecraft that have enough capacity for the crew, material and fuel needed to stop and return, and that can keep the crew alive long enough for a return trip.
Is there a theoretical possibility for a manned mission to reach that point with existing launch systems and spacecraft, possibly after ad-hoc modifications? (I'm aware that NASA says it is not an option but we are more agile and inventive than that, right?)
I suppose StarShip, potentially with minor modifications, could do the job hands down; anything before that?