In that case you'd only have a different IP if you hit the localhost port of that tunneled connection, not everything on your computer. Unless you set up your browser and mail to proxy through that port there wouldn't be any issue with "switching IPs".

This isn't what happens - you do a port forward and you access your services through localhost:port. Nothing else goes through the tunnel. Endpoint services see the ec2 ip. There is no IP "switching" or risk of getting banned.

But if your ec2 service has security group access to multiple things it's extremely useful because you can hit localhost:xxxx for postgres, localhost:yyyy for elasticsearch, etc.

This wouldn't be efficient in my case. I'm testing a frontend that's served on localhost:80 and connects to a local backend also on localhost:80 that makes DB calls to some remote database on 3306. I'd have to modify the backend code to connect through the proxy port every time I wanted to test it. As it is the backend code on my computer is a mirror of the production environment. Normally if I tunnel I have it set up to forward everything through the tunnel except localhost.

In this case you'd simply do the tunnel for 3306:3306.

Your frontend and backend code would run locally and connect to MySQL through the proxy. You wouldn't have to change any backend configuration.