Speaking from a union perspective . . . If there is a push to change working practices, Terms & Conditions, etc. and you don't feel comfortable about overtly objecting make sure to at least say something, like, "I'd like time to think about that".
Saying nothing can legitimately be taken by management as "silent assent". This is important if the suggestion constitutes a proposed change in your Terms & Conditions of employment.
Actually complying with a change constitutes agreeing to a change in your contract of employment.
(Your contract is no longer what is written down if you voluntarily vary it by complying with a requested change. The change does not need to be written down as an update to your written contract. If you later stop doing whatever it is you complied with then you risk being found in breach of contract.)
If there is an existing Policy you can refer to that might be helpful. For example, if it is suggested that everyone should wear badges showing "preferred pronouns" (real issue in another current thread), you could say, "But that would have to go into the Uniform Policy first? So we couldn't do it now even if we wanted to."
Your Terms & Conditions also include "custom and practice". For example, if it is suggested that because there is no policy on Single Sex Staff Changing Rooms then there is no problem making them mixed sex, you could say, "There is no written policy but it is custom and practice - so all staff would have to agree, not just us here. I wouldn't want to get the Unions / Staff Council down our necks if we jump the gun on this"
In my experience many HR staff are clueless about what existing HR Policies and Procedures actually say. (Someone else on Mumsnet had a right go at me when I said this before so I can only say that I am speaking honestly from my experience.)
Don't feel bad if HR claim that something is already covered by existing policies or does not conflict with them. You could just say, "I didn't realise that - maybe we should still check if it affects the Impact Assessment though? It seems like it might from what has been suggested."
Whatever sort of NHS Trust you are working in there are bound to be different patient groups plus different clinical and non-clinical areas and staff groups with different needs. One size rarely fits all. As appropriate, you could say, "Have we thought about how this might affect (whatever)" or "This sounds like it would affect patients so we really should run it past PALS first. Perhaps they could do a patient survey?"
Are issues around POVA or Child Protection in parts of the Trust?
There are bound to be potential conflicts of legal rights if the interests of only one staff or patient group is considered in isolation. You could say, "I know lots of women are worried about some of these things. Could HR organise a forum for female staff, to come up with ideas to make sure that the Trust does not accidentally fall foul of the law, by breaching any of its obligations to female staff under the Equalities Act?"
If you don't already know who your union Rep is and what their attitude is on these issues it is worth finding out. Most NHS staff have a choice of unions to join so you might want to shop around if you think you would get better support from a different union.
(Nationally they are all pretty useless at considering Women's Rights in this area but local Branches and Reps can vary a lot.)
I hope some of these ideas are helpful @ViciousTrollop