Good point. Perhaps a modification can be made that is restricted to generally safe characters, then you can add your own stuff as the website demands. Which then leaves you to remember which stuff you need to add, on every site - so not that great.

Or there could be several modes and a database of websites that automatically picks a mode based on the website. Which leaves you remembering modes in the worst case scenario, or trying a few of them out.

I think an acceptable solution can be made by analysing the password requirements of the top N websites, then coming up with a good scheme that works on most, and an alternate scheme that works on the rest. One mistake is usually allowed everywhere.