I had the same problem - I wanted to change a certain parameter in several photos to the same value.
I found 2 ways:
As rob j crowe said - you need to edit the photo not in the Develop tab, but in the Library. There, all change is RELATIVE, not ABSOLUTE.
Use the plugin Relative Adjustments.lrplugin.
For a start, you can use its trial version (it does the ...