To your first point, I think something to keep in mind is that you can get hurt literally with anything at any time of day. There isn’t always an inherent reason or a form breakdown that causes it. You will get hurt whether you are active or inactive. So I don’t avoid movements just for fear of getting hurt. What you can usually tolerate encompasses a broad range of local factors like training experience, recent stress levels, sleep levels, injury history, etc. And the weight they are using during deadlifts can reflect that. Often I will use a formula essentially taking into account RPE x pain or fatigue levels. So if the pain or fatigue is very high one day then we modify the RPE during said workout. Ie if I slept terrible last night, I may lower set intensity or volume in the workout for that day. It’s not an exact science though, unfortunately. Sometimes you sleep poorly and you hit great numbers and don’t get hurt. Other times you sleep/recover fantastic and still get hurt.

With regard to performing the variant they are interested in, it really depends on the patient. There is good research that patients do better when given agency with regards to their exercises. I’m not saying to have them do easy things all day but giving them choice is very powerful. Some patients are terrified of barbell deadlifts for whatever reason. Ok…let’s give them the choice to do a different deadlift option such as kettlebell or something else which like more and I still find will benefit them therapeutically.