I want to be able to direct copy and paste the connection string without any modification on our end

Connections
1

For example on SSH I would like to set the login be replaced with something else by default ?
Example : ssh -l pi proxy25.rt3.io -p 34200 or ssh://pi@proxy25.rt3.io:34200

2

You can find information on how to set this globally for your user or per service in this support article:
https://link.remote.it/support/connection-settings