If what you mean is "this policy sounds reasonable, but I cannot sign anything sight unseen" any reasonable HR will just print (scan / email) you a copy of anything they want you to sign. My 2c.
If the company actually cares about keeping you and they have any sort of leeway as to changing the policy, they will listen to why you can't agree to it.
I agree in spirit, but I suspect this would almost never happen: companies who care and track employee signatures on a bunch of HR policies tend to be large and inflexible (smaller companies would often make some blanket blurb "thou must read and comply to policies that you can find <here>" and move on -- they have technologies to develop).
Using your leverage as an employer to change the terms of the agreement immediately after the agreement has been made is unacceptable. It might be legal¹, but that doesn't make it right. And when you present subsequent legal agreements after I've started my employment that I "must" sign when I explicitly asked for them up front (and even when my employment agreement states that this is "the entire agreement" too!) — I mean, the company might as well put on their best impression of Darth Vader "pray I do not alter it further".
There's also the point about asking for HR to send you a copy. I actually did that in the case above, and it just never happened; HR wants you to go through the website, for everything. It's incredible how dead set some people can be, because "that's the system"! The entire thing was inane, and so fell by the wayside, and was forgotten about. About a year later, someone new took over, audited their predecessor, found out I hadn't signed, and sent an email "Hey, we noticed you never signed that you've read the pamphlet, can you sign?" and attached the pamphlet as a PDF to that email. Since that rectified the error (I now had a copy of the pamphlet) a signature was given and life went on.
¹IANAL. I honestly don't think "we won't fire you" should be valid as consideration in a contract. Thus, such agreements lack consideration, so they're not valid contracts, signature or not. I think some Canadian courts have agreed with this, but alas, I'm not in Canada. I'm still at-will, so IDK if it really matters per se, given what at-will is.
If you consider only what has changed from the original agreement: the company gets whatever it is you're signing the document for. You typically get nothing, aside from getting to keep your job. It's in this second agreement that I just don't find a compelling argument that "keep your job" (i.e., wages) suffices as "consideration". If you do, it's effectively reneging on the original deal, and trying to replace it with a new one that's not as good for the employee. Meanwhile, the employee has likely left their previous employment, and is at a huge disadvantage to walk away at this point. Particularly so when a prospective employee asks for anything that requires a signature up front, and when the documents in question use legalese like "this is the entire agreement". After that, there shouldn't be any more agreements unless something actually changes.