I’ve written before about this on this forum, but when SQ a couple of years ago (starting in 2023) tried or actually did introduce new fees (custodoy fee based on AUM above some threshold), I wrote them a polite message
- asking them to either waive the fees or wave goodbye my assets
- that I wasn’t interested in a discussion with them and that they should just escalate to their necessary management level able to make that call and let me know of their decision
Heard back within two weeks that they would leave me on their flat rate for that year and refund me the additional custody charges already charged by crediting me with a corresponding trading fee credit as compensation for the additional fee already charged, but that they couldn’t guarantee that they would keep this arrangement with me in the years following (they have so far).
Fine with me – I also won’t guarantee them I’ll stay with them if they make another move in charging me more based on my AUM with them. 
I don’t feel bad about this at all: their trading fees are still outrageous (compared to, say, IBKR), and their “Swissness” label is really just a fig leaf and marketing label (IMO).1
[1] I have also written about this elsewhere on this forum, search for 'sub-custodian' and '@Your_Full_Name' if you're interested in the technical details of what happens to "your" assets when some dumb orange utan were to yank the chain on your assets, or search for "swiss broker" if you're interested in a more