I already own my own domain name, and it is pointed at several different IPs already for various things (email, IRC, etc.)

If I choose to switch to your hosting, will it lose all my current IP settings? I am currently using register.com as the domain host.

We can configure your DNS settings as you want. Also you can hold your domain with name servers of your domain registrar and don't switch it on our name servers. Some our customers have external mail servers and there is no probem with it. If you are reseller you can configure DNS settings of your domain yourself in web reseller panel.

There is no options to sign up for the Profi plan without Transferring the domain, and I am kind of wary about doing that as I already have settings that I don't want to lose just for signing up for a webpage.

Please chose

'I already own this domain. Please transfer it for FREE.'

and your domain won't be transfered from the current domain name registrar.

And finally each domain name transfer should be confirm by domain name administrator - YOU, otherwise it would easyu to transfer yahoo.com here and there
So, everything is under your control.