Hi Luboš,
Regarding the first issue, we do have an extension restriction but for some reason it’s not working, I need to debug to see what’s wrong with it.
After you upload your s/mime .pfx or .p12 file and apply, there you should see to buttons one for exporting the certificate and another to delete the certificate.
I will let you know as soon as I fixed the extension issue.
Best regards,
Hadi