Thanks loukash and carl123 for explaining the progression of the "select same name" feature which has culminated in a workable compromise for me now and hopefully others.
As explained in a previous post, like many others who have wanted to adopt Affinity Publisher coming from Adobe InDesign, we've been hampered by the lack of global layer support. I have a number of documents that have hundreds of pages with separate layers for different content, such as the original scan of a document on one layer, the transcription of the text on a second layer, an English translation on a third layer etc. I need to be able to switch each layer on and off on all pages across the whole document at once. I've always been able to import the document into Publisher but until now there has been no way I could show or hide each existing layer across the whole document with a couple of clicks. So after over three years of owning Publisher it is only now capable of doing what I need it to do, which is why it is a big deal to me but I understand why others may not be as excited, and of course proper global layer support would be ideal.
Using master pages is not a solution that has or will ever work for me. At least now I have a way I can continue to work on my documents from InDesign in Publisher, but I still look forward to the day that we get proper "global layers".
To answer your exact question quoted above though: I don't want to change anything on pages globally, each page is unique (different typefaces, sizes, colours etc), which is why master pages are not a solution. However, if I wanted to, having used "select same name" to select all my layers with the same name on every page, I can change properties such as opacity, colour etc. The reason InDesign and other desktop publishing software has "global layers" is to have grouped content across pages that can be switched on and off, reordered and locked/unlocked. Now in Designer I can switch the layers on/off and lock/unlock across the whole document, I just can't reorder the layers globally. Again, this is now a workable compromise for me, and I expect others, until layers finally become truly global.