Picture something that cannot be changed:
speed of light?
our mortality?
the fact that girls don't possess a Y chromosome?
(It's a testament to how far science has come that as I write these examples, I'm thinking, "Hmmm, maybe this COULD be changed")
Anyway, assuming we can't change the speed of light, our mortality, or girls' having two X chromosomes ...
Can we undermine any of those things?
Can you undermine the speed of light? Can you undermine our impending death?
It's not like going faster / slower undermines the speed of light. It still is the same ol' 300,000 km /sec. It's not like extending your life span undermines its finite nature.
I think, as you surmised, you're picturing real world uses of 'undermine' that are more synonymous with "in opposition to / disapproval of / differing goals"?
I probably have a more narrow definition of 'undermine' as "to make worse / to make harder". With THAT definition, undermining something always changes it.
To your broader question, YES you'll definitely have to be flexible with how you interpret utterances of words that can imply different things in different contexts. And also, remind yourself that the question stem asks "which can MOST reasonably be concluded", not "which one MUST be true".
That difference always buys you a little looseness with language.