Thank you for the update.
When FlashFXP starts up what version of OpenSSL does it report in the status window.
You don't need to rename any of the dll files, you can switch the version using a custom command
Ctrl+R or From the main menu > Command > Raw Command
To use OpenSSL 1.1.0 use the command
Code:
/set app.openssl 1.1.0
To use OpenSSL 1.0.2 use the command
Code:
/set app.openssl 1.0.2
Then restart FlashFXP
There might be an unknown error with client certificates when using OpenSSL 1.1.0, I will look into this and let you know what I find.